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Pretty version of the draft OAuth spec
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oauth-v2.html
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<title>draft-ietf-oauth-v2-31 - The OAuth 2.0 Authorization Framework</title>
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<style>body { string-set: short-title "OAuth 2.0" }</style>
<article>
<section class="titlepage">
<div class=page-header>
<h1>
The OAuth 2.0 Authorization Framework
<small>draft-ietf-oauth-v2-31</small>
</h1>
</div>
<section id="abstract" class="abstract">
<h2>Abstract</h2>
<p>
The OAuth 2.0 authorization framework enables a third-party application to obtain limited
access to an HTTP service, either on behalf of a resource owner by orchestrating an approval
interaction between the resource owner and the HTTP service, or by allowing the third-party
application to obtain access on its own behalf. This specification replaces and obsoletes
the OAuth 1.0 protocol described in RFC 5849.
</p>
</section>
<section class="authors">
<h3>Authors:</h3>
<ol>
<li class="vcard">
<a href="http://dickhardt.org/" class="url fn">Dick Hardt</a>,
<span class="org">Microsoft</span>
(editor)
<a href="mailto:[email protected]" class="email">[email protected]</a>
</li>
</ol>
</section>
</section>
<aside>
<ol class=toc>
<li>draft-ietf-oauth-v2-31</li>
<li><a href="#introduction">Introduction</a></li>
<ol>
<li><a href="#roles">Roles</a></li>
<li><a href="#protocol-flow">Protocol Flow</a></li>
<li><a href="#authorization-grant">Authorization Grant</a></li>
<li><a href="#access-token">Access Token</a></li>
<li><a href="#refresh-token">Refresh Token</a></li>
<li><a href="#tls">TLS Version</a></li>
<li><a href="#http-redirections">HTTP Redirections</a></li>
<li><a href="#interoperability">Interoperability</a></li>
<li><a href="#notational-conventions">Notational Conventions</a></li>
</ol>
<li><a href="#client-registration">Client Registration</a></li>
<ol>
<li><a href="#client-types">Client Types</a></li>
<li><a href="#client-identifier">Client Identifier</a></li>
<li><a href="#client-authentication">Client Authentication</a></li>
<li><a href="#unregistered-clients">Unregistered Clients</a></li>
</ol>
<li><a href="#protocol-endpoints">Protocol Endpoints</a></li>
<ol>
<li><a href="#authorization-endpoint">Authorization Endpoint</a></li>
<li><a href="#token-endpoint">Token Endpoint</a></li>
<li><a href="#scope">Access Token Scope</a></li>
</ol>
<li><a href="#obtaining-authorization">Obtaining Authorization</a></li>
<ol>
<li><a href="#grant-code">Authorization Code Grant</a></li>
<li><a href="#grant-implicit">Implicit Grant</a></li>
<li><a href="#grant-password">Resource Owner Password Credentials Grant</a></li>
<li><a href="#grant-client">Client Credentials Grant</a></li>
<li><a href="#ext-grant">Extension Grants</a></li>
</ol>
<li><a href="#token-issue">Issuing an Access Token</a></li>
<ol>
<li><a href="#token-response">Successful Response</a></li>
<li><a href="#token-errors">Error Response</a></li>
</ol>
<li><a href="#token-refresh">Refreshing an Access Token</a></li>
<ol></ol>
<li><a href="#access-resource">Accessing Protected Resources</a></li>
<ol>
<li><a href="#token-types">Access Token Types</a></li>
<li><a href="#resource-errors">Error Response</a></li>
</ol>
<li><a href="#extensions">Extensibility</a></li>
<ol>
<li><a href="#new-types">Defining Access Token Types</a></li>
<li><a href="#endpoint-params">Defining New Endpoint Parameters</a></li>
<li><a href="#defining-new-authorization-grant-types">Defining New Authorization Grant Types</a></li>
<li><a href="#response-type-ext">Defining New Authorization Endpoint Response Types</a></li>
<li><a href="#new-errors">Defining Additional Error Codes</a></li>
</ol>
<li><a href="#NativeApps">Native Applications</a></li>
<ol></ol>
<li><a href="#security-considerations">Security Considerations</a></li>
<ol>
<li><a href="#client-authentication">Client Authentication</a></li>
<li><a href="#client-impersonation">Client Impersonation</a></li>
<li><a href="#AccessTokenSecurity">Access Tokens</a></li>
<li><a href="#refresh-tokens">Refresh Tokens</a></li>
<li><a href="#authorization-codes">Authorization Codes</a></li>
<li><a href="#authorization-code-redirection-uri-manipulation">Authorization Code Redirection URI Manipulation</a></li>
<li><a href="#resource-owner-password-credentials">Resource Owner Password Credentials</a></li>
<li><a href="#request-confidentiality">Request Confidentiality</a></li>
<li><a href="#endpoints-authenticity">Endpoints Authenticity</a></li>
<li><a href="#anthropy">Credentials Guessing Attacks</a></li>
<li><a href="#phishing-attacks">Phishing Attacks</a></li>
<li><a href="#CSRF">Cross-Site Request Forgery</a></li>
<li><a href="#clickjacking">Clickjacking</a></li>
<li><a href="#code-injection-and-input-validation">Code Injection and Input Validation</a></li>
<li><a href="#open-redirect">Open Redirectors</a></li>
<li><a href="#ImplicitImpersonation">Misuse of Access Token to Impersonate Resource Owner in Implicit Flow</a></li>
</ol>
<li><a href="#iana-considerations">IANA Considerations</a></li>
<ol>
<li><a href="#type-registry">OAuth Access Token Type Registry</a></li>
<li><a href="#parameters-registry">OAuth Parameters Registry</a></li>
<li><a href="#response-type-registry">OAuth Authorization Endpoint Response Type Registry</a></li>
<li><a href="#error-registry">OAuth Extensions Error Registry</a></li>
</ol>
</ol>
</aside>
<section id="introduction">
<h2>Introduction</h2>
<p>
In the traditional client-server authentication model, the client requests an access
restricted resource (protected resource) on the server by authenticating with the server
using the resource owner's credentials. In order to provide third-party applications access
to restricted resources, the resource owner shares its credentials with the third-party.
This creates several problems and limitations:
</p>
<ul class="symbols">
<li> <p>
Third-party applications are required to store the resource owner's credentials
for future use, typically a password in clear-text.
</p>
</li>
<li> <p>
Servers are required to support password authentication, despite the security
weaknesses inherent in passwords.
</p>
</li>
<li> <p>
Third-party applications gain overly broad access to the resource owner's protected
resources, leaving resource owners without any ability to restrict duration or access
to a limited subset of resources.
</p>
</li>
<li> <p>
Resource owners cannot revoke access to an individual third-party without revoking
access to all third-parties, and must do so by changing their password.
</p>
</li>
<li> <p>
Compromise of any third-party application results in compromise of the end-user's
password and all of the data protected by that password.
</p>
</li>
</ul>
<p>
OAuth addresses these issues by introducing an authorization layer and separating the role
of the client from that of the resource owner. In OAuth, the client requests access to
resources controlled by the resource owner and hosted by the resource server, and is issued
a different set of credentials than those of the resource owner.
</p>
<p>
Instead of using the resource owner's credentials to access protected resources, the client
obtains an access token - a string denoting a specific scope, lifetime, and other access
attributes. Access tokens are issued to third-party clients by an authorization server with
the approval of the resource owner. The client uses the access token to access the
protected resources hosted by the resource server.
</p>
<p>
For example, an end-user (resource owner) can grant a printing service (client) access
to her protected photos stored at a photo sharing service (resource server), without
sharing her username and password with the printing service. Instead, she authenticates
directly with a server trusted by the photo sharing service (authorization server), which
issues the printing service delegation-specific credentials (access token).
</p>
<p>
This specification is designed for use with HTTP (<a href="#rfc2616">RFC2616</a>). The use of
OAuth over any other protocol than HTTP is out of scope.
</p>
<p>
The OAuth 1.0 protocol (<a href="#rfc5849">RFC5849</a>), published as an informational document,
was the result of a small ad-hoc community effort. This standards-track specification builds
on the OAuth 1.0 deployment experience, as well as additional use cases and extensibility
requirements gathered from the wider IETF community. The OAuth 2.0 protocol is not backward
compatible with OAuth 1.0. The two versions may co-exist on the network and implementations
may choose to support both. However, it is the intention of this specification that new
implementation support OAuth 2.0 as specified in this document, and that OAuth 1.0 is used
only to support existing deployments. The OAuth 2.0 protocol shares very few implementation
details with the OAuth 1.0 protocol. Implementers familiar with OAuth 1.0 should approach
this document without any assumptions as to its structure and details.
</p>
<section id="roles">
<h3>Roles</h3>
<p>
OAuth defines four roles:
</p>
<dl>
<dt>resource owner</dt>
<dd> <p>
An entity capable of granting access to a protected resource. When the resource owner
is a person, it is referred to as an end-user.
</p>
</dd>
<dt>resource server</dt>
<dd> <p>
The server hosting the protected resources, capable of accepting and responding to
protected resource requests using access tokens.
</p>
</dd>
<dt>client</dt>
<dd> <p>
An application making protected resource requests on behalf of the resource owner and
with its authorization. The term client does not imply any particular implementation
characteristics (e.g. whether the application executes on a server, a desktop, or
other devices).
</p>
</dd>
<dt>authorization server</dt>
<dd> <p>
The server issuing access tokens to the client after successfully authenticating the
resource owner and obtaining authorization.
</p>
</dd>
</dl>
<p>
The interaction between the authorization server and resource server is beyond the scope
of this specification. The authorization server may be the same server as the resource
server or a separate entity. A single authorization server may issue access tokens
accepted by multiple resource servers.
</p>
</section>
<section id="protocol-flow">
<h3>Protocol Flow</h3>
<figure id="figure-1">
<figcaption>Abstract Protocol Flow</figcaption>
<pre>
+--------+ +---------------+
| |--(A)- Authorization Request -&gt;| Resource |
| | | Owner |
| |&lt;-(B)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(C)-- Authorization Grant --&gt;| Authorization |
| Client | | Server |
| |&lt;-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------&gt;| Resource |
| | | Server |
| |&lt;-(F)--- Protected Resource ---| |
+--------+ +---------------+</pre>
</figure>
<p>
The abstract OAuth 2.0 flow illustrated in <a href="#figure-1">Abstract Protocol Flow</a> describes the interaction
between the four roles and includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The client requests authorization from the resource owner. The authorization request
can be made directly to the resource owner (as shown), or preferably indirectly via
the authorization server as an intermediary.
</p>
</li>
<li> <p>
The client receives an authorization grant, which is a credential representing
the resource owner's authorization, expressed using one of four grant types defined
in this specification or using an extension grant type. The authorization grant type
depends on the method used by the client to request authorization and the types
supported by the authorization server.
</p>
</li>
<li> <p>
The client requests an access token by authenticating with the authorization server
and presenting the authorization grant.
</p>
</li>
<li> <p>
The authorization server authenticates the client and validates the authorization
grant, and if valid issues an access token.
</p>
</li>
<li> <p>
The client requests the protected resource from the resource server and authenticates
by presenting the access token.
</p>
</li>
<li> <p>
The resource server validates the access token, and if valid, serves the request.
</p>
</li>
</ol>
<p>
The preferred method for the client to obtain an authorization grant from the resource
owner (depicted in steps (A) and (B)) is to use the authorization server as an intermediary,
which is illustrated in <a href="#figure-3">Authorization Code Flow</a>.
</p>
</section>
<section id="authorization-grant">
<h3>Authorization Grant</h3>
<p>
An authorization grant is a credential representing the resource owner's authorization
(to access its protected resources) used by the client to obtain an access token. This
specification defines four grant types: authorization code, implicit, resource owner
password credentials, and client credentials, as well as an extensibility mechanism for
defining additional types.
</p>
<section id="authorization-code">
<h4>Authorization Code</h4>
<p>
The authorization code is obtained by using an authorization server as an intermediary
between the client and resource owner. Instead of requesting authorization directly
from the resource owner, the client directs the resource owner to an authorization
server (via its user-agent as defined in <a href="#rfc2616">RFC2616</a>), which in turn
directs the resource owner back to the client with the authorization code.
</p>
<p>
Before directing the resource owner back to the client with the authorization code, the
authorization server authenticates the resource owner and obtains authorization.
Because the resource owner only authenticates with the authorization server, the
resource owner's credentials are never shared with the client.
</p>
<p>
The authorization code provides a few important security benefits such as the ability
to authenticate the client, and the transmission of the access token directly to
the client without passing it through the resource owner's user-agent, potentially
exposing it to others, including the resource owner.
</p>
</section>
<section id="ImplicitIntro">
<h4>Implicit</h4>
<p>
The implicit grant is a simplified authorization code flow optimized for clients
implemented in a browser using a scripting language such as JavaScript. In the implicit
flow, instead of issuing the client an authorization code, the client is issued an
access token directly (as the result of the resource owner authorization). The grant
type is implicit as no intermediate credentials (such as an authorization code) are
issued (and later used to obtain an access token).
</p>
<p>
When issuing an access token during the implicit grant flow, the authorization server
does not authenticate the client. In some cases, the client identity can be verified
via the redirection URI used to deliver the access token to the client. The access
token may be exposed to the resource owner or other applications with access to the
resource owner's user-agent.
</p>
<p>
Implicit grants improve the responsiveness and efficiency of some clients (such as a
client implemented as an in-browser application) since it reduces the number of round
trips required to obtain an access token. However, this convenience should be weighed
against the security implications of using implicit grants,
such as those described in <a href="#accesstokensecurity">Access Tokens</a> and
<a href="#implicitimpersonation">Misuse of Access Token to Impersonate Resource Owner in Implicit Flow</a>,
especially when the authorization code grant type is available.
</p>
</section>
<section id="resource-owner-password-credentials">
<h4>Resource Owner Password Credentials</h4>
<p>
The resource owner password credentials (i.e. username and password) can be used
directly as an authorization grant to obtain an access token. The credentials should
only be used when there is a high degree of trust between the resource owner and the
client (e.g. the client is part of the device operating system or a highly privileged
application), and when other authorization grant types are not available (such as an
authorization code).
</p>
<p>
Even though this grant type requires direct client access to the resource owner
credentials, the resource owner credentials are used for a single request and are
exchanged for an access token. This grant type can eliminate the need for the client
to store the resource owner credentials for future use, by exchanging the credentials
with a long-lived access token or refresh token.
</p>
</section>
<section id="client-credentials">
<h4>Client Credentials</h4>
<p>
The client credentials (or other forms of client authentication) can be used as an
authorization grant when the authorization scope is limited to the protected resources
under the control of the client, or to protected resources previously arranged with the
authorization server. Client credentials are used as an authorization grant typically
when the client is acting on its own behalf (the client is also the resource owner), or
is requesting access to protected resources based on an authorization previously
arranged with the authorization server.
</p>
</section>
</section>
<section id="access-token">
<h3>Access Token</h3>
<p>
Access tokens are credentials used to access protected resources. An access token is a
string representing an authorization issued to the client. The string is usually opaque
to the client. Tokens represent specific scopes and durations of access, granted by the
resource owner, and enforced by the resource server and authorization server.
</p>
<p>
The token may denote an identifier used to retrieve the authorization information, or
self-contain the authorization information in a verifiable manner (i.e. a token string
consisting of some data and a signature). Additional authentication credentials, which
are beyond the scope of this specification, may be required in order for the client to
use a token.
</p>
<p>
The access token provides an abstraction layer, replacing different authorization
constructs (e.g. username and password) with a single token understood by the resource
server. This abstraction enables issuing access tokens more restrictive than the
authorization grant used to obtain them, as well as removing the resource server's need to
understand a wide range of authentication methods.
</p>
<p>
Access tokens can have different formats, structures, and methods of utilization (e.g.
cryptographic properties) based on the resource server security requirements. Access token
attributes and the methods used to access protected resources are beyond the scope of this
specification and are defined by companion specifications.
</p>
</section>
<section id="refresh-token">
<h3>Refresh Token</h3>
<p>
Refresh tokens are credentials used to obtain access tokens. Refresh tokens are issued to
the client by the authorization server and are used to obtain a new access token when the
current access token becomes invalid or expires, or to obtain additional access tokens
with identical or narrower scope (access tokens may have a shorter lifetime and fewer
permissions than authorized by the resource owner). Issuing a refresh token is optional
at the discretion of the authorization server. If the authorization server issues a
refresh token, it is included when issuing an access token (i.e. step (D) in
<a href="#figure-1">Abstract Protocol Flow</a>).
</p>
<p>
A refresh token is a string representing the authorization granted to the client by the
resource owner. The string is usually opaque to the client. The token denotes an
identifier used to retrieve the authorization information. Unlike access tokens, refresh
tokens are intended for use only with authorization servers and are never sent to
resource servers.
</p>
<figure id="figure-2">
<figcaption>Refreshing an Expired Access Token</figcaption>
<pre>
+--------+ +---------------+
| |--(A)------- Authorization Grant ---------&gt;| |
| | | |
| |&lt;-(B)----------- Access Token -------------| |
| | &amp; Refresh Token | |
| | | |
| | +----------+ | |
| |--(C)---- Access Token ----&gt;| | | |
| | | | | |
| |&lt;-(D)- Protected Resource --| Resource | | Authorization |
| Client | | Server | | Server |
| |--(E)---- Access Token ----&gt;| | | |
| | | | | |
| |&lt;-(F)- Invalid Token Error -| | | |
| | +----------+ | |
| | | |
| |--(G)----------- Refresh Token -----------&gt;| |
| | | |
| |&lt;-(H)----------- Access Token -------------| |
+--------+ &amp; Optional Refresh Token +---------------+</pre>
</figure>
<p>
The flow illustrated in <a href="#figure-2">Refreshing an Expired Access Token</a> includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The client requests an access token by authenticating with the authorization server,
and presenting an authorization grant.
</p>
</li>
<li> <p>
The authorization server authenticates the client and validates the authorization
grant, and if valid issues an access token and a refresh token.
</p>
</li>
<li> <p>
The client makes a protected resource request to the resource server by presenting
the access token.
</p>
</li>
<li> <p>
The resource server validates the access token, and if valid, serves the request.
</p>
</li>
<li> <p>
Steps (C) and (D) repeat until the access token expires. If the client knows the
access token expired, it skips to step (G), otherwise it makes another protected
resource request.
</p>
</li>
<li> <p>
Since the access token is invalid, the resource server returns an invalid token
error.
</p>
</li>
<li> <p>
The client requests a new access token by authenticating with the authorization
server and presenting the refresh token. The client authentication requirements are
based on the client type and on the authorization server policies.
</p>
</li>
<li> <p>
The authorization server authenticates the client and validates the refresh token,
and if valid issues a new access token (and optionally, a new refresh token).
</p>
</li>
</ol>
<p>
Steps C, D, E, and F are outside the scope of this specification as described in
<a href="#access-resource">Accessing Protected Resources</a>.
</p>
</section>
<section id="tls">
<h3>TLS Version</h3>
<p>
Whenever TLS is used by this specification, the appropriate version (or versions) of
TLS will vary over time, based on the widespread deployment and known security
vulnerabilities. At the time of this writing, TLS version 1.2 <a href="#rfc5246">RFC5246</a>
is the most recent version, but has a very limited deployment base and might not be
readily available for implementation. TLS version 1.0 <a href="#rfc2246">RFC2246</a> is the
most widely deployed version, and will provide the broadest interoperability.
</p>
<p>
Implementations MAY also support additional transport-layer security mechanisms
that meet their security requirements.
</p>
</section>
<section id="http-redirections">
<h3>HTTP Redirections</h3>
<p>
This specification makes extensive use of HTTP redirections, in which the client or the
authorization server directs the resource owner's user-agent to another destination. While
the examples in this specification show the use of the HTTP 302 status code, any other
method available via the user-agent to accomplish this redirection is allowed and is
considered to be an implementation detail.
</p>
</section>
<section id="interoperability">
<h3>Interoperability</h3>
<p>
OAuth 2.0 provides a rich authorization framework with well-defined security properties.
However, as a rich and highly extensible framework with many optional components, on its
own, this specification is likely to produce a wide range of non-interoperable
implementations.
</p>
<p>
In addition, this specification leaves a few required components partially or fully
undefined (e.g. client registration, authorization server capabilities, endpoint
discovery). Without these components, clients must be manually and specifically
configured against a specific authorization server and resource server in order to
interoperate.
</p>
<p>
This framework was designed with the clear expectation that future work will define
prescriptive profiles and extensions necessary to achieve full web-scale
interoperability.
</p>
</section>
<section id="notational-conventions">
<h3>Notational Conventions</h3>
<p>
The key words &quot;MUST&quot;, &quot;MUST NOT&quot;, &quot;REQUIRED&quot;, &quot;SHALL&quot;, &quot;SHALL NOT&quot;, &quot;SHOULD&quot;, &quot;SHOULD
NOT&quot;, &quot;RECOMMENDED&quot;, &quot;MAY&quot;, and &quot;OPTIONAL&quot; in this specification are to be interpreted as
described in <a href="#rfc2119">RFC2119</a>.
</p>
<p>
This specification uses the Augmented Backus-Naur Form (ABNF) notation of
<a href="#rfc5234">RFC5234</a>.
Additionally, the rule URI-Reference is included from
Uniform Resource Identifier (URI) <a href="#rfc3986">RFC3986</a>.
</p>
<p>
Certain security-related terms are to be understood in the sense defined in
<a href="#rfc4949">RFC4949</a>. These terms include, but are not limited to, &quot;attack&quot;,
&quot;authentication&quot;, &quot;authorization&quot;, &quot;certificate&quot;, &quot;confidentiality&quot;, &quot;credential&quot;,
&quot;encryption&quot;, &quot;identity&quot;, &quot;sign&quot;, &quot;signature&quot;, &quot;trust&quot;, &quot;validate&quot;, and &quot;verify&quot;.
</p>
<p>
Unless otherwise noted, all the protocol parameter names and values are case sensitive.
</p>
</section>
</section>
<section id="client-registration">
<h2>Client Registration</h2>
<p>
Before initiating the protocol, the client registers with the authorization server. The
means through which the client registers with the authorization server are beyond the
scope of this specification, but typically involve end-user interaction with an HTML
registration form.
</p>
<p>
Client registration does not require a direct interaction between the client and the
authorization server. When supported by the authorization server, registration can rely
on other means for establishing trust and obtaining the required client properties (e.g.
redirection URI, client type). For example, registration can be accomplished using a
self-issued or third-party-issued assertion, or by the authorization server performing
client discovery using a trusted channel.
</p>
<p>
When registering a client, the client developer SHALL:
</p>
<ul class="symbols">
<li> <p>
specify the client type as described in <a href="#client-types">Client Types</a>,
</p>
</li>
<li> <p>
provide its client redirection URIs as described in
<a href="#redirect-uri">Redirection Endpoint</a>, and
</p>
</li>
<li> <p>
include any other information required by the authorization server (e.g. application
name, website, description, logo image, the acceptance of legal terms).
</p>
</li>
</ul>
<section id="client-types">
<h3>Client Types</h3>
<p>
OAuth defines two client types, based on their ability to authenticate securely with the
authorization server (i.e. ability to maintain the confidentiality of their client
credentials):
</p>
<dl>
<dt>confidential</dt>
<dd> <p>
Clients capable of maintaining the confidentiality of their credentials (e.g.
client implemented on a secure server with restricted access to the client
credentials), or capable of secure client authentication using other means.
</p>
</dd>
<dt>public</dt>
<dd> <p>
Clients incapable of maintaining the confidentiality of their credentials (e.g.
clients executing on the device used by the resource owner such as an installed
native application or a web browser-based application), and incapable of secure
client authentication via any other means.
</p>
</dd>
</dl>
<p>
The client type designation is based on the authorization server's definition of secure
authentication and its acceptable exposure levels of client credentials. The
authorization server SHOULD NOT make assumptions about the client type.
</p>
<p>
A client may be implemented as a distributed set of components, each with a different
client type and security context (e.g. a distributed client with both a confidential
server-based component and a public browser-based component). If the authorization server
does not provide support for such clients, or does not provide guidance with regard to
their registration, the client SHOULD register each component as a separate client.
</p>
<p>
This specification has been designed around the following client profiles:
</p>
<dl>
<dt>web application</dt>
<dd> <p>
A web application is a confidential client running on a web server. Resource owners
access the client via an HTML user interface rendered in a user-agent on the device
used by the resource owner. The client credentials as well as any access token issued
to the client are stored on the web server and are not exposed to or accessible by
the resource owner.
</p>
</dd>
<dt>user-agent-based application</dt>
<dd> <p>
A user-agent-based application is a public client in which the client code is
downloaded from a web server and executes within a user-agent (e.g. web browser) on
the device used by the resource owner. Protocol data and credentials are easily
accessible (and often visible) to the resource owner. Since such applications reside
within the user-agent, they can make seamless use of the user-agent capabilities when
requesting authorization.
</p>
</dd>
<dt>native application</dt>
<dd> <p>
A native application is a public client installed and executed on the device used by
the resource owner. Protocol data and credentials are accessible to the resource
owner. It is assumed that any client authentication credentials included in the
application can be extracted. On the other hand, dynamically issued credentials such
as access tokens or refresh tokens can receive an acceptable level of protection. At a
minimum, these credentials are protected from hostile servers with which the
application may interact with. On some platforms these credentials might be protected
from other applications residing on the same device.
</p>
</dd>
</dl>
</section>
<section id="client-identifier">
<h3>Client Identifier</h3>
<p>
The authorization server issues the registered client a client identifier - a unique
string representing the registration information provided by the client. The client
identifier is not a secret; it is exposed to the resource owner, and MUST NOT be used
alone for client authentication. The client identifier is unique to the authorization
server.
</p>
<p>
The client identifier string size is left undefined by this specification. The client
should avoid making assumptions about the identifier size. The authorization server
SHOULD document the size of any identifier it issues.
</p>
</section>
<section id="client-authentication">
<h3>Client Authentication</h3>
<p>
If the client type is confidential, the client and authorization server establish a client
authentication method suitable for the security requirements of the authorization server.
The authorization server MAY accept any form of client authentication meeting its
security requirements.
</p>
<p>
Confidential clients are typically issued (or establish) a set of client credentials used for
authenticating with the authorization server (e.g. password, public/private key pair).
</p>
<p>
The authorization server MAY establish a client authentication method with public clients.
However, the authorization server MUST NOT rely on public client authentication for the
purpose of identifying the client.
</p>
<p>
The client MUST NOT use more than one authentication method in each request.
</p>
<section id="client-password">
<h4>Client Password</h4>
<p>
Clients in possession of a client password MAY use the HTTP Basic authentication scheme
as defined in <a href="#rfc2617">RFC2617</a> to authenticate with the authorization server.
The client identifier is encoded using the
application/x-www-form-urlencoded
encoding algorithm per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a> and the encoded value is
used as the username; the client password is encoded using
the same algorithm and used as the
password. The authorization server MUST support the HTTP Basic authentication scheme
for authenticating clients that were issued a client password.
</p>
<figure>
<p class="preamble">
For example (with extra line breaks for display purposes only):
</p>
<pre>
Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3</pre>
</figure>
<p>
Alternatively, the authorization server MAY support including the client credentials in
the request body using the following parameters:
</p>
<dl>
<dt>client_id</dt>
<dd> <p>
REQUIRED. The client identifier issued to the client during the registration process
described by <a href="#client-identifier">Client Identifier</a>.
</p>
</dd>
<dt>client_secret</dt>
<dd> <p>
REQUIRED. The client secret. The client MAY omit the parameter if the client secret
is an empty string.
</p>
</dd>
</dl>
<p>
Including the client credentials in the request body using the two parameters is NOT
RECOMMENDED, and SHOULD be limited to clients unable to directly utilize the HTTP Basic
authentication scheme (or other password-based HTTP authentication schemes). The
parameters can only be transmitted in the request body and MUST NOT be included in the
request URI.
</p>
<figure>
<p class="preamble">
For example, requesting to refresh an access token (<a href="#token-refresh">Refreshing an Access Token</a>)
using the body parameters (with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&amp;refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
&amp;client_id=s6BhdRkqt3&amp;client_secret=7Fjfp0ZBr1KtDRbnfVdmIw</pre>
</figure>
<p>
The authorization server MUST require the use of TLS as described in
<a href="#tls">TLS Version</a> when sending requests using password authentication.
</p>
<p>
Since this client authentication method involves a password, the authorization server
MUST protect any endpoint utilizing it against brute force attacks.
</p>
</section>
<section id="other-authentication-methods">
<h4>Other Authentication Methods</h4>
<p>
The authorization server MAY support any suitable HTTP authentication scheme matching
its security requirements. When using other authentication methods, the authorization
server MUST define a mapping between the client identifier (registration record) and
authentication scheme.
</p>
</section>
</section>
<section id="unregistered-clients">
<h3>Unregistered Clients</h3>
<p>
This specification does not exclude the use of unregistered clients. However, the use
with such clients is beyond the scope of this specification, and requires additional
security analysis and review of its interoperability impact.
</p>
</section>
</section>
<section id="protocol-endpoints">
<h2>Protocol Endpoints</h2>
<p>
The authorization process utilizes two authorization server endpoints (HTTP resources):
</p>
<ul class="symbols">
<li> <p>
Authorization endpoint - used by the client to obtain authorization from the resource
owner via user-agent redirection.
</p>
</li>
<li> <p>
Token endpoint - used by the client to exchange an authorization grant for an access
token, typically with client authentication.
</p>
</li>
</ul>
<p>
As well as one client endpoint:
</p>
<ul class="symbols">
<li> <p>
Redirection endpoint - used by the authorization server to return authorization
credentials responses to the client via the resource owner user-agent.
</p>
</li>
</ul>
<p>
Not every authorization grant type utilizes both endpoints. Extension grant types MAY
define additional endpoints as needed.
</p>
<section id="authorization-endpoint">
<h3>Authorization Endpoint</h3>
<p>
The authorization endpoint is used to interact with the resource owner and obtain
an authorization grant. The authorization server MUST first verify the identity of the
resource owner. The way in which the authorization server authenticates the resource
owner (e.g. username and password login, session cookies) is beyond the scope of this
specification.
</p>
<p>
The means through which the client obtains the location of the authorization endpoint are
beyond the scope of this specification, but the location is typically provided in the
service documentation.
</p>
<p>
The endpoint URI MAY include an
application/x-www-form-urlencoded formatted
(per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>) query component (<a href="#rfc3986">RFC3986</a>
section 3.4), which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
</p>
<p>
Since requests to the authorization endpoint result in user authentication and the
transmission of clear-text credentials (in the HTTP response), the authorization server
MUST require the use of TLS as described in <a href="#tls">TLS Version</a> when sending requests
to the authorization endpoint.
</p>
<p>
The authorization server MUST support the use of the HTTP GET
method <a href="#rfc2616">RFC2616</a> for the authorization endpoint, and MAY support the use
of the POST method as well.
</p>
<p>
Parameters sent without a value MUST be treated as if they were omitted from the request.
The authorization server MUST ignore unrecognized request parameters. Request and
response parameters MUST NOT be included more than once.
</p>
<section id="response-type">
<h4>Response Type</h4>
<p>
The authorization endpoint is used by the authorization code grant type and implicit
grant type flows. The client informs the authorization server of the desired grant
type using the following parameter:
</p>
<dl>
<dt>response_type</dt>
<dd> <p>
REQUIRED. The value MUST be one of code for requesting
an authorization code as described by <a href="#code-authz-req">Authorization Request</a>,
token for requesting an access token (implicit grant)
as described by <a href="#implicit-authz-req">Authorization Request</a>, or a registered extension
value as described by <a href="#response-type-ext">Defining New Authorization Endpoint Response Types</a>.
</p>
</dd>
</dl>
<p>
Extension response types MAY contain a space-delimited (%x20) list of values, where the
order of values does not matter (e.g. response type a b is
the same as b a). The meaning of such composite response
types is defined by their respective specifications.
</p>
<p>
If an authorization request is missing the response_type
parameter, or if the response type is not understood, the authorization server MUST
return an error response as described in <a href="#code-authz-error">Error Response</a>.
</p>
</section>
<section id="redirect-uri">
<h4>Redirection Endpoint</h4>
<p>
After completing its interaction with the resource owner, the authorization server
directs the resource owner's user-agent back to the client. The authorization server
redirects the user-agent to the client's redirection endpoint previously established
with the authorization server during the client registration process or when making
the authorization request.
</p>
<p>
The redirection endpoint URI MUST be an absolute URI as defined by
<a href="#rfc3986">RFC3986</a> section 4.3. The endpoint URI MAY include an
application/x-www-form-urlencoded formatted
(per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>) query component (<a href="#rfc3986">RFC3986</a>
section 3.4), which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
</p>
<section id="endpoint-request-confidentiality">
<h5>Endpoint Request Confidentiality</h5>
<p>
The redirection endpoint SHOULD require the use of TLS as described in
<a href="#tls">TLS Version</a> when the requested response type is
code or token, or
when the redirection request will result in the transmission of sensitive credentials
over an open network. This specification does not mandate the use of TLS because at
the time of this writing, requiring clients to deploy TLS is a significant hurdle for
many client developers. If TLS is not available, the authorization server SHOULD warn
the resource owner about the insecure endpoint prior to redirection (e.g. display a
message during the authorization request).
</p>
<p>
Lack of transport-layer security can have a severe impact on the security of the
client and the protected resources it is authorized to access. The use of
transport-layer security is particularly critical when the authorization process is
used as a form of delegated end-user authentication by the client (e.g. third-party
sign-in service).
</p>
</section>
<section id="registration-requirements">
<h5>Registration Requirements</h5>
<p>
The authorization server MUST require the following clients to register their
redirection endpoint:
</p>
<ul class="symbols">
<li> <p>
Public clients.
</p>
</li>
<li> <p>
Confidential clients utilizing the implicit grant type.
</p>
</li>
</ul>
<p>
The authorization server SHOULD require all clients to register their redirection
endpoint prior to utilizing the authorization endpoint.
</p>
<p>
The authorization server SHOULD require the client to provide the complete
redirection URI (the client MAY use the state request
parameter to achieve per-request customization). If requiring the registration of
the complete redirection URI is not possible, the authorization server SHOULD require
the registration of the URI scheme, authority, and path (allowing the client to
dynamically vary only the query component of the redirection URI when requesting
authorization).
</p>
<p>
The authorization server MAY allow the client to register multiple redirection
endpoints.
</p>
<p>
Lack of a redirection URI registration requirement can enable an attacker to use
the authorization endpoint as open redirector as described in
<a href="#open-redirect">Open Redirectors</a>.
</p>
</section>
<section id="dynamic-configuration">
<h5>Dynamic Configuration</h5>
<p>
If multiple redirection URIs have been registered, if only part of the redirection
URI has been registered, or if no redirection URI has been registered, the client
MUST include a redirection URI with the authorization request using the
redirect_uri request parameter.
</p>
<p>
When a redirection URI is included in an authorization request, the authorization
server MUST compare and match the value received against at least one of the
registered redirection URIs (or URI components) as defined in
<a href="#rfc3986">RFC3986</a> section 6, if any redirection URIs were registered.
If the client registration included the full redirection URI, the authorization
server MUST compare the two URIs using simple string comparison as defined
in <a href="#rfc3986">RFC3986</a> section 6.2.1.
</p>
</section>
<section id="invalid-endpoint">
<h5>Invalid Endpoint</h5>
<p>
If an authorization request fails validation due to a missing, invalid, or
mismatching redirection URI, the authorization server SHOULD inform the resource
owner of the error, and MUST NOT automatically redirect the user-agent to the invalid
redirection URI.
</p>
</section>
<section id="endpoint-content">
<h5>Endpoint Content</h5>
<p>
The redirection request to the client's endpoint typically results in an HTML
document response, processed by the user-agent. If the HTML response is served
directly as the result of the redirection request, any script included in the HTML
document will execute with full access to the redirection URI and the credentials it
contains.
</p>
<p>
The client SHOULD NOT include any third-party scripts (e.g. third-party analytics,
social plug-ins, ad networks) in the redirection endpoint response. Instead, it
SHOULD extract the credentials from the URI and redirect the user-agent again to
another endpoint without exposing the credentials (in the URI or elsewhere). If
third-party scripts are included, the client MUST ensure that its own scripts
(used to extract and remove the credentials from the URI) will execute first.
</p>
</section>
</section>
</section>
<section id="token-endpoint">
<h3>Token Endpoint</h3>
<p>
The token endpoint is used by the client to obtain an access token by presenting its
authorization grant or refresh token. The token endpoint is used with every authorization
grant except for the implicit grant type (since an access token is issued directly).
</p>
<p>
The means through which the client obtains the location of the token endpoint are
beyond the scope of this specification but is typically provided in the service
documentation.
</p>
<p>
The endpoint URI MAY include an
application/x-www-form-urlencoded formatted
(per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>) query component (<a href="#rfc3986">RFC3986</a>
section 3.4), which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
</p>
<p>
Since requests to the token endpoint result in the transmission of clear-text credentials
(in the HTTP request and response), the authorization server MUST require the use of TLS
as described in <a href="#tls">TLS Version</a> when sending requests to the token endpoint.
</p>
<p>
The client MUST use the HTTP POST method when making access
token requests.
</p>
<p>
Parameters sent without a value MUST be treated as if they were omitted from the request.
The authorization server MUST ignore unrecognized request parameters. Request and
response parameters MUST NOT be included more than once.
</p>
<section id="token-endpoint-auth">
<h4>Client Authentication</h4>
<p>
Confidential clients or other clients issued client credentials MUST authenticate with
the authorization server as described in <a href="#client-authentication">Client Authentication</a> when
making requests to the token endpoint. Client authentication is used for:
</p>
<ul class="symbols">
<li> <p>
Enforcing the binding of refresh tokens and authorization codes to the client they
were issued to. Client authentication is critical when an authorization code is
transmitted to the redirection endpoint over an insecure channel, or when the
redirection URI has not been registered in full.
</p>
</li>
<li> <p>
Recovering from a compromised client by disabling the client or changing its
credentials, thus preventing an attacker from abusing stolen refresh tokens. Changing
a single set of client credentials is significantly faster than revoking an entire
set of refresh tokens.
</p>
</li>
<li> <p>
Implementing authentication management best practices, which require periodic
credential rotation. Rotation of an entire set of refresh tokens can be
challenging, while rotation of a single set of client credentials is significantly
easier.
</p>
</li>
</ul>
<p>
A client MAY use the
client_id request parameter to identify itself when sending
requests to the token endpoint.
In the authorization_code
grant_type request to the token endpoint,
an unauthenticated client MUST send its
client_id to prevent itself from
inadvertently accepting a code intended for a client with a different
client_id. This protects the client from substitution of the
authentication code. (It provides no additional security for the
protected resource.)
</p>
</section>
</section>
<section id="scope">
<h3>Access Token Scope</h3>
<p>
The authorization and token endpoints allow the client to specify the scope of the access
request using the scope request parameter. In turn, the
authorization server uses the scope response parameter to
inform the client of the scope of the access token issued.
</p>
<p>
The value of the scope parameter is expressed as a list of space-delimited, case
sensitive strings. The strings are defined by the authorization server. If the value
contains multiple space-delimited strings, their order does not matter, and each string
adds an additional access range to the requested scope.
</p>
<figure>
<pre>
scope = scope-token *( SP scope-token )
scope-token = 1*( %x21 / %x23-5B / %x5D-7E )</pre>
</figure>
<p>
The authorization server MAY fully or partially ignore the scope requested by the client
based on the authorization server policy or the resource owner's instructions. If the
issued access token scope is different from the one requested by the client, the
authorization server MUST include the scope response
parameter to inform the client of the actual scope granted.
</p>
<p>
If the client omits the scope parameter when requesting authorization, the authorization
server MUST either process the request using a pre-defined default value, or fail the
request indicating an invalid scope. The authorization server SHOULD document its scope
requirements and default value (if defined).
</p>
</section>
</section>
<section id="obtaining-authorization">
<h2>Obtaining Authorization</h2>
<p>
To request an access token, the client obtains authorization from the resource owner. The
authorization is expressed in the form of an authorization grant, which the client uses to
request the access token. OAuth defines four grant types: authorization code, implicit,
resource owner password credentials, and client credentials. It also provides an extension
mechanism for defining additional grant types.
</p>
<section id="grant-code">
<h3>Authorization Code Grant</h3>
<p>
The authorization code grant type is used to obtain both access tokens and refresh
tokens and is optimized for confidential clients. As a redirection-based flow, the client
must be capable of interacting with the resource owner's user-agent (typically a web
browser) and capable of receiving incoming requests (via redirection) from the
authorization server.
</p>
<figure id="figure-3">
<figcaption>Authorization Code Flow</figcaption>
<pre>
+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+----(A)-- &amp; Redirection URI ----&gt;| |
| User- | | Authorization |
| Agent -+----(B)-- User authenticates ---&gt;| Server |
| | | |
| -+----(C)-- Authorization Code ---&lt;| |
+-|----|---+ +---------------+
| | ^ v
(A) (C) | |
| | | |
^ v | |
+---------+ | |
| |&gt;---(D)-- Authorization Code ---------' |
| Client | &amp; Redirection URI |
| | |
| |&lt;---(E)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)</pre>
<p class="postamble">
Note: The lines illustrating steps A, B, and C are broken into two parts as they pass
through the user-agent.
</p>
</figure>
<p>
The flow illustrated in <a href="#figure-3">Authorization Code Flow</a> includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The client initiates the flow by directing the resource owner's user-agent to the
authorization endpoint. The client includes its client identifier, requested
scope, local state, and a redirection URI to which the authorization server will send
the user-agent back once access is granted (or denied).
</p>
</li>
<li> <p>
The authorization server authenticates the resource owner (via the user-agent) and
establishes whether the resource owner grants or denies the client's access request.
</p>
</li>
<li> <p>
Assuming the resource owner grants access, the authorization server redirects the
user-agent back to the client using the redirection URI provided earlier (in the
request or during client registration). The redirection URI includes an authorization
code and any local state provided by the client earlier.
</p>
</li>
<li> <p>
The client requests an access token from the authorization server's token endpoint
by including the authorization code received in the previous step. When making the
request, the client authenticates with the authorization server. The client includes
the redirection URI used to obtain the authorization code for verification.
</p>
</li>
<li> <p>
The authorization server authenticates the client, validates the authorization code,
and ensures the redirection URI received matches the URI used to redirect the client
in step (C). If valid, the authorization server responds back with an access token
and optionally, a refresh token.
</p>
</li>
</ol>
<section id="code-authz-req">
<h4>Authorization Request</h4>
<p>
The client constructs the request URI by adding the following parameters to the
query component of the authorization endpoint URI using the
application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>response_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to code.
</p>
</dd>
<dt>client_id</dt>
<dd> <p>
REQUIRED. The client identifier as described in
<a href="#client-identifier">Client Identifier</a>.
</p>
</dd>
<dt>redirect_uri</dt>
<dd> <p>
OPTIONAL. As described in <a href="#redirect-uri">Redirection Endpoint</a>.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL. The scope of the access request as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
<dt>state</dt>
<dd> <p>
RECOMMENDED. An opaque value used by the client to maintain state between the request
and callback. The authorization server includes this value when redirecting the
user-agent back to the client. The parameter SHOULD be used for preventing
cross-site request forgery as described in <a href="#csrf">Cross-Site Request Forgery</a>.
</p>
</dd>
</dl>
<p>
The client directs the resource owner to the constructed URI using an HTTP redirection
response, or by other means available to it via the user-agent.
</p>
<figure>
<p class="preamble">
For example, the client directs the user-agent to make the following HTTP request
using TLS (with extra line breaks for display purposes only):
</p>
<pre>
GET /authorize?response_type=code&amp;client_id=s6BhdRkqt3&amp;state=xyz
&amp;redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com</pre>
</figure>
<p>
The authorization server validates the request to ensure all required parameters are
present and valid. If the request is valid, the authorization server authenticates the
resource owner and obtains an authorization decision (by asking the resource owner or
by establishing approval via other means).
</p>
<p>
When a decision is established, the authorization server directs the user-agent to the
provided client redirection URI using an HTTP redirection response, or by other means
available to it via the user-agent.
</p>
</section>
<section id="code-authz-resp">
<h4>Authorization Response</h4>
<p>
If the resource owner grants the access request, the authorization server issues an
authorization code and delivers it to the client by adding the following parameters to
the query component of the redirection URI using the
application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>code</dt>
<dd> <p>
REQUIRED. The authorization code generated by the authorization server. The
authorization code MUST expire shortly after it is issued to mitigate the risk of
leaks. A maximum authorization code lifetime of 10 minutes is RECOMMENDED. The
client MUST NOT use the authorization code more than once. If an authorization code
is used more than once, the authorization server MUST deny the request and SHOULD
revoke (when possible) all tokens previously issued based on that authorization
code. The authorization code is bound to the client identifier and redirection URI.
</p>
</dd>
<dt>state</dt>
<dd> <p>
REQUIRED if the state parameter was present in the
client authorization request. The exact value received from the client.
</p>
</dd>
</dl>
<figure>
<p class="preamble">
For example, the authorization server redirects the user-agent by sending the
following HTTP response:
</p>
<pre>
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA
&amp;state=xyz</pre>
</figure>
<p>
The client MUST ignore unrecognized response parameters. The authorization code
string size is left undefined by this specification. The client should avoid making
assumptions about code value sizes. The authorization server SHOULD document the size
of any value it issues.
</p>
<section id="code-authz-error">
<h5>Error Response</h5>
<p>
If the request fails due to a missing, invalid, or mismatching redirection URI, or if
the client identifier is missing or invalid, the authorization server SHOULD inform
the resource owner of the error, and MUST NOT automatically redirect the user-agent
to the invalid redirection URI.
</p>
<p>
If the resource owner denies the access request or if the request fails for reasons
other than a missing or invalid redirection URI, the authorization server informs the
client by adding the following parameters to the query component of the redirection
URI using the application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>error</dt>
<dd> <p>
REQUIRED. A single ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> error code from the following:
</p>
<dl>
<dt>invalid_request</dt>
<dd> <p>
The request is missing a required parameter, includes an invalid
parameter value, includes a parameter more than once, or is otherwise
malformed.
</p>
</dd>
<dt>unauthorized_client</dt>
<dd> <p>
The client is not authorized to request an authorization code using this
method.
</p>
</dd>
<dt>access_denied</dt>
<dd> <p>
The resource owner or authorization server denied the request.
</p>
</dd>
<dt>unsupported_response_type</dt>
<dd> <p>
The authorization server does not support obtaining an authorization code
using this method.
</p>
</dd>
<dt>invalid_scope</dt>
<dd> <p>
The requested scope is invalid, unknown, or malformed.
</p>
</dd>
<dt>server_error</dt>
<dd> <p>
The authorization server encountered an unexpected condition that prevented
it from fulfilling the request.
(This error code is needed because a 500 Internal Server Error
HTTP status code cannot be returned to the client
via a HTTP redirect.)
</p>
</dd>
<dt>temporarily_unavailable</dt>
<dd> <p>
The authorization server is currently unable to handle the request due to a
temporary overloading or maintenance of the server.
(This error code is needed because a 503 Service Unavailable
HTTP status code cannot be returned to the client
via a HTTP redirect.)
</p>
</dd>
</dl>
<p>
Values for the error parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_description</dt>
<dd> <p>
OPTIONAL. A human-readable ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> text providing additional information,
used to assist the client developer in understanding the error that occurred.
Values for the error_description parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_uri</dt>
<dd> <p>
OPTIONAL. A URI identifying a human-readable web page with information about the
error, used to provide the client developer with additional information about the
error.
Values for the error_uri parameter
MUST conform to the URI-Reference syntax, and thus MUST NOT include
characters outside the set %x21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>state</dt>
<dd> <p>
REQUIRED if a state parameter was present in the
client authorization request. The exact value received from the client.
</p>
</dd>
</dl>
<figure>
<p class="preamble">
For example, the authorization server redirects the user-agent by sending the
following HTTP response:
</p>
<pre>
HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied&amp;state=xyz</pre>
</figure>
</section>
</section>
<section id="token-req">
<h4>Access Token Request</h4>
<p>
The client makes a request to the token endpoint by sending the following parameters
using the application/x-www-form-urlencoded format
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a> with a character encoding of UTF-8
in the HTTP request entity-body:
</p>
<dl>
<dt>grant_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to authorization_code.
</p>
</dd>
<dt>code</dt>
<dd> <p>
REQUIRED. The authorization code received from the authorization server.
</p>
</dd>
<dt>redirect_uri</dt>
<dd> <p>
REQUIRED, if the redirect_uri parameter was included in
the authorization request as described in <a href="#code-authz-req">Authorization Request</a>, and
their values MUST be identical.
</p>
</dd>
<dt>client_id</dt>
<dd> <p>
REQUIRED, if the client is not authenticating with the
authorization server as described in <a href="#token-endpoint-auth">Client Authentication</a>.
</p>
</dd>
</dl>
<p>
If the client type is confidential or the client was issued client credentials (or
assigned other authentication requirements), the client MUST authenticate with the
authorization server as described in <a href="#token-endpoint-auth">Client Authentication</a>.
</p>
<figure>
<p class="preamble">
For example, the client makes the following HTTP request using TLS
(with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&amp;code=SplxlOBeZQQYbYS6WxSbIA
&amp;redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb</pre>
</figure>
<p>
The authorization server MUST:
</p>
<ul class="symbols">
<li> <p>
require client authentication for confidential clients or for any client that was
issued client credentials (or with other authentication requirements),
</p>
</li>
<li> <p>
authenticate the client if client authentication is included,
</p>
</li>
<li> <p>
ensure the authorization code was issued to the authenticated
confidential client, or if the client is public, ensure the code was issued to
client_id in the request,
</p>
</li>
<li> <p>
verify that the authorization code is valid, and
</p>
</li>
<li> <p>
ensure that the redirect_uri parameter is present if
the redirect_uri parameter was included in the initial
authorization request as described in <a href="#code-authz-req">Authorization Request</a>, and if
included ensure their values are identical.
</p>
</li>
</ul>
</section>
<section id="access-token-response">
<h4>Access Token Response</h4>
<p>
If the access token request is valid and authorized, the authorization server issues an
access token and optional refresh token as described in <a href="#token-response">Successful Response</a>.
If the request client authentication failed or is invalid, the authorization server returns
an error response as described in <a href="#token-errors">Error Response</a>.
</p>
<figure>
<p class="preamble">
An example successful response:
</p>
<pre>
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
&quot;access_token&quot;:&quot;2YotnFZFEjr1zCsicMWpAA&quot;,
&quot;token_type&quot;:&quot;example&quot;,
&quot;expires_in&quot;:3600,
&quot;refresh_token&quot;:&quot;tGzv3JOkF0XG5Qx2TlKWIA&quot;,
&quot;example_parameter&quot;:&quot;example_value&quot;
}</pre>
</figure>
</section>
</section>
<section id="grant-implicit">
<h3>Implicit Grant</h3>
<p>
The implicit grant type is used to obtain access tokens (it does not support the issuance
of refresh tokens) and is optimized for public clients known to operate a particular
redirection URI. These clients are typically implemented in a browser using a scripting
language such as JavaScript.
</p>
<p>
As a redirection-based flow, the client must be capable of interacting with the
resource owner's user-agent (typically a web browser) and capable of receiving incoming
requests (via redirection) from the authorization server.
</p>
<p>
Unlike the authorization code grant type in which the client makes separate requests for
authorization and access token, the client receives the access token as the result of the
authorization request.
</p>
<p>
The implicit grant type does not include client authentication, and relies on the
presence of the resource owner and the registration of the redirection URI. Because the
access token is encoded into the redirection URI, it may be exposed to the resource owner
and other applications residing on the same device.
</p>
<figure id="figure-4">
<figcaption>Implicit Grant Flow</figcaption>
<pre>
+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+----(A)-- &amp; Redirection URI ---&gt;| |
| User- | | Authorization |
| Agent -|----(B)-- User authenticates --&gt;| Server |
| | | |
| |&lt;---(C)--- Redirection URI ----&lt;| |
| | with Access Token +---------------+
| | in Fragment
| | +---------------+
| |----(D)--- Redirection URI ----&gt;| Web-Hosted |
| | without Fragment | Client |
| | | Resource |
| (F) |&lt;---(E)------- Script ---------&lt;| |
| | +---------------+
+-|--------+
| |
(A) (G) Access Token
| |
^ v
+---------+
| |
| Client |
| |
+---------+</pre>
<p class="postamble">
Note: The lines illustrating steps A and B are broken into two parts as they pass
through the user-agent.
</p>
</figure>
<p>
The flow illustrated in <a href="#figure-4">Implicit Grant Flow</a> includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The client initiates the flow by directing the resource owner's user-agent to the
authorization endpoint. The client includes its client identifier, requested
scope, local state, and a redirection URI to which the authorization server will send
the user-agent back once access is granted (or denied).
</p>
</li>
<li> <p>
The authorization server authenticates the resource owner (via the user-agent) and
establishes whether the resource owner grants or denies the client's access request.
</p>
</li>
<li> <p>
Assuming the resource owner grants access, the authorization server redirects the
user-agent back to the client using the redirection URI provided earlier. The
redirection URI includes the access token in the URI fragment.
</p>
</li>
<li> <p>
The user-agent follows the redirection instructions by making a request to the
web-hosted client resource (which does not include the fragment per
<a href="#rfc2616">RFC2616</a>). The user-agent retains the fragment information locally.
</p>
</li>
<li> <p>
The web-hosted client resource returns a web page (typically an HTML document with an
embedded script) capable of accessing the full redirection URI including the fragment
retained by the user-agent, and extracting the access token (and other parameters)
contained in the fragment.
</p>
</li>
<li> <p>
The user-agent executes the script provided by the web-hosted client resource
locally, which extracts the access token and passes it to the client.
</p>
</li>
</ol>
<p>
See <a href="#implicitintro">Implicit</a> and <a href="#nativeapps">Native Applications</a>
for background on using the implicit grant.
See <a href="#accesstokensecurity">Access Tokens</a> and <a href="#implicitimpersonation">Misuse of Access Token to Impersonate Resource Owner in Implicit Flow</a>
for important security considerations when using the implicit grant.
</p>
<section id="implicit-authz-req">
<h4>Authorization Request</h4>
<p>
The client constructs the request URI by adding the following parameters to the
query component of the authorization endpoint URI using the
application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>response_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to token.
</p>
</dd>
<dt>client_id</dt>
<dd> <p>
REQUIRED. The client identifier as described in
<a href="#client-identifier">Client Identifier</a>.
</p>
</dd>
<dt>redirect_uri</dt>
<dd> <p>
OPTIONAL. As described in <a href="#redirect-uri">Redirection Endpoint</a>.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL. The scope of the access request as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
<dt>state</dt>
<dd> <p>
RECOMMENDED. An opaque value used by the client to maintain state between the request
and callback. The authorization server includes this value when redirecting the
user-agent back to the client. The parameter SHOULD be used for preventing
cross-site request forgery as described in <a href="#csrf">Cross-Site Request Forgery</a>.
</p>
</dd>
</dl>
<p>
The client directs the resource owner to the constructed URI using an HTTP redirection
response, or by other means available to it via the user-agent.
</p>
<figure>
<p class="preamble">
For example, the client directs the user-agent to make the following HTTP request
using TLS (with extra line breaks for display purposes only):
</p>
<pre>
GET /authorize?response_type=token&amp;client_id=s6BhdRkqt3&amp;state=xyz
&amp;redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com</pre>
</figure>
<p>
The authorization server validates the request to ensure all required parameters are
present and valid. The authorization server MUST verify that the redirection URI to which
it will redirect the access token matches a redirection URI registered by the client as
described in <a href="#redirect-uri">Redirection Endpoint</a>.
</p>
<p>
If the request is valid, the authorization server authenticates the resource owner and
obtains an authorization decision (by asking the resource owner or by establishing
approval via other means).
</p>
<p>
When a decision is established, the authorization server directs the user-agent to the
provided client redirection URI using an HTTP redirection response, or by other means
available to it via the user-agent.
</p>
</section>
<section id="implicit-authz-resp">
<h4>Access Token Response</h4>
<p>
If the resource owner grants the access request, the authorization server issues an
access token and delivers it to the client by adding the following parameters to
the fragment component of the redirection URI using the
application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>access_token</dt>
<dd> <p>
REQUIRED. The access token issued by the authorization server.
</p>
</dd>
<dt>token_type</dt>
<dd> <p>
REQUIRED. The type of the token issued as described in
<a href="#token-types">Access Token Types</a>. Value is case insensitive.
</p>
</dd>
<dt>expires_in</dt>
<dd> <p>
RECOMMENDED. The lifetime in seconds of the access token. For example, the value
3600 denotes that the access token will expire in one
hour from the time the response was generated. If omitted, the authorization server
SHOULD provide the expiration time via other means or document the default value.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL, if identical to the scope requested by the client, otherwise REQUIRED. The
scope of the access token as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
<dt>state</dt>
<dd> <p>
REQUIRED if the state parameter was present in the
client authorization request. The exact value received from the client.
</p>
</dd>
</dl>
<p>
The authorization server MUST NOT issue a refresh token.
</p>
<figure>
<p class="preamble">
For example, the authorization server redirects the user-agent by sending the
following HTTP response (with extra line breaks for display purposes only):
</p>
<pre>
HTTP/1.1 302 Found
Location: http://example.com/cb#access_token=2YotnFZFEjr1zCsicMWpAA
&amp;state=xyz&amp;token_type=example&amp;expires_in=3600</pre>
<p class="postamble">
Developers should note that some user-agents do not support the inclusion of a
fragment component in the HTTP Location response header
field. Such clients will require using other methods for redirecting the client than
a 3xx redirection response. For example, returning an HTML page that includes a
'continue' button with an action linked to the redirection URI.
</p>
</figure>
<p>
The client MUST ignore unrecognized response parameters. The access token string size
is left undefined by this specification. The client should avoid making assumptions
about value sizes. The authorization server SHOULD document the size of any value it
issues.
</p>
<section id="implicit-authz-error">
<h5>Error Response</h5>
<p>
If the request fails due to a missing, invalid, or mismatching redirection URI, or if
the client identifier is missing or invalid, the authorization server SHOULD inform
the resource owner of the error, and MUST NOT automatically redirect the user-agent
to the invalid redirection URI.
</p>
<p>
If the resource owner denies the access request or if the request fails for reasons
other than a missing or invalid redirection URI, the authorization server informs the
client by adding the following parameters to the fragment component of the
redirection URI using the
application/x-www-form-urlencoded format,
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a>:
</p>
<dl>
<dt>error</dt>
<dd> <p>
REQUIRED. A single ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> error code from the following:
</p>
<dl>
<dt>invalid_request</dt>
<dd> <p>
The request is missing a required parameter, includes an invalid
parameter value, includes a parameter more than once, or is otherwise malformed.
</p>
</dd>
<dt>unauthorized_client</dt>
<dd> <p>
The client is not authorized to request an access token using this method.
</p>
</dd>
<dt>access_denied</dt>
<dd> <p>
The resource owner or authorization server denied the request.
</p>
</dd>
<dt>unsupported_response_type</dt>
<dd> <p>
The authorization server does not support obtaining an access token using
this method.
</p>
</dd>
<dt>invalid_scope</dt>
<dd> <p>
The requested scope is invalid, unknown, or malformed.
</p>
</dd>
<dt>server_error</dt>
<dd> <p>
The authorization server encountered an unexpected condition that prevented
it from fulfilling the request.
(This error code is needed because a 500 Internal Server Error
HTTP status code cannot be returned to the client
via a HTTP redirect.)
</p>
</dd>
<dt>temporarily_unavailable</dt>
<dd> <p>
The authorization server is currently unable to handle the request due to a
temporary overloading or maintenance of the server.
(This error code is needed because a 503 Service Unavailable
HTTP status code cannot be returned to the client
via a HTTP redirect.)
</p>
</dd>
</dl>
<p>
Values for the error parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_description</dt>
<dd> <p>
OPTIONAL. A human-readable ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> text providing additional information,
used to assist the client developer in understanding the error that occurred.
Values for the error_description parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_uri</dt>
<dd> <p>
OPTIONAL. A URI identifying a human-readable web page with information about the
error, used to provide the client developer with additional information about the
error.
Values for the error_uri parameter
MUST conform to the URI-Reference syntax, and thus MUST NOT include
characters outside the set %x21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>state</dt>
<dd> <p>
REQUIRED if a state parameter was present in the
client authorization request. The exact value received from the client.
</p>
</dd>
</dl>
<figure>
<p class="preamble">
For example, the authorization server redirects the user-agent by sending the
following HTTP response:
</p>
<pre>
HTTP/1.1 302 Found
Location: https://client.example.com/cb#error=access_denied&amp;state=xyz</pre>
</figure>
</section>
</section>
</section>
<section id="grant-password">
<h3>Resource Owner Password Credentials Grant</h3>
<p>
The resource owner password credentials grant type is suitable in cases where the
resource owner has a trust relationship with the client, such as the device operating
system or a highly privileged application. The authorization server should take special
care when enabling this grant type, and only allow it when other flows are not viable.
</p>
<p>
The grant type is suitable for clients capable of obtaining the resource owner's
credentials (username and password, typically using an interactive form). It is also used
to migrate existing clients using direct authentication schemes such as HTTP Basic or
Digest authentication to OAuth by converting the stored credentials to an access token.
</p>
<figure id="figure-5">
<figcaption>Resource Owner Password Credentials Flow</figcaption>
<pre>
+----------+
| Resource |
| Owner |
| |
+----------+
v
| Resource Owner
(A) Password Credentials
|
v
+---------+ +---------------+
| |&gt;--(B)---- Resource Owner -------&gt;| |
| | Password Credentials | Authorization |
| Client | | Server |
| |&lt;--(C)---- Access Token ---------&lt;| |
| | (w/ Optional Refresh Token) | |
+---------+ +---------------+</pre>
</figure>
<p>
The flow illustrated in <a href="#figure-5">Resource Owner Password Credentials Flow</a> includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The resource owner provides the client with its username and password.
</p>
</li>
<li> <p>
The client requests an access token from the authorization server's token endpoint by
including the credentials received from the resource owner. When making the request,
the client authenticates with the authorization server.
</p>
</li>
<li> <p>
The authorization server authenticates the client and validates the resource owner
credentials, and if valid issues an access token.
</p>
</li>
</ol>
<section id="authorization-request-and-response">
<h4>Authorization Request and Response</h4>
<p>
The method through which the client obtains the resource owner credentials is beyond
the scope of this specification. The client MUST discard the credentials once an access
token has been obtained.
</p>
</section>
<section id="password-tok-req">
<h4>Access Token Request</h4>
<p>
The client makes a request to the token endpoint by adding the following parameters
using the application/x-www-form-urlencoded format
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a> with a character encoding of UTF-8
in the HTTP request entity-body:
</p>
<dl>
<dt>grant_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to password.
</p>
</dd>
<dt>username</dt>
<dd> <p>
REQUIRED. The resource owner username.
</p>
</dd>
<dt>password</dt>
<dd> <p>
REQUIRED. The resource owner password.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL. The scope of the access request as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
</dl>
<p>
If the client type is confidential or the client was issued client credentials (or
assigned other authentication requirements), the client MUST authenticate with the
authorization server as described in <a href="#token-endpoint-auth">Client Authentication</a>.
</p>
<figure>
<p class="preamble">
For example, the client makes the following HTTP request using transport-layer
security (with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=password&amp;username=johndoe&amp;password=A3ddj3w</pre>
</figure>
<p>
The authorization server MUST:
</p>
<ul class="symbols">
<li> <p>
require client authentication for confidential clients or for any client that was
issued client credentials (or with other authentication requirements),
</p>
</li>
<li> <p>
authenticate the client if client authentication is included, and
</p>
</li>
<li> <p>
validate the resource owner password credentials using its existing password
validation algorithm.
</p>
</li>
</ul>
<p>
Since this access token request utilizes the resource owner's password, the
authorization server MUST protect the endpoint against brute force attacks (e.g. using
rate-limitation or generating alerts).
</p>
</section>
<section id="access-token-response">
<h4>Access Token Response</h4>
<p>
If the access token request is valid and authorized, the authorization server issues an
access token and optional refresh token as described in <a href="#token-response">Successful Response</a>.
If the request failed client authentication or is invalid, the authorization server returns
an error response as described in <a href="#token-errors">Error Response</a>.
</p>
<figure>
<p class="preamble">
An example successful response:
</p>
<pre>
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
&quot;access_token&quot;:&quot;2YotnFZFEjr1zCsicMWpAA&quot;,
&quot;token_type&quot;:&quot;example&quot;,
&quot;expires_in&quot;:3600,
&quot;refresh_token&quot;:&quot;tGzv3JOkF0XG5Qx2TlKWIA&quot;,
&quot;example_parameter&quot;:&quot;example_value&quot;
}</pre>
</figure>
</section>
</section>
<section id="grant-client">
<h3>Client Credentials Grant</h3>
<p>
The client can request an access token using only its client credentials (or other
supported means of authentication) when the client is requesting access to the
protected resources under its control, or those of another resource owner that have been
previously arranged with the authorization server (the method of which is beyond the
scope of this specification).
</p>
<p>
The client credentials grant type MUST only be used by confidential clients.
</p>
<figure id="figure-6">
<figcaption>Client Credentials Flow</figcaption>
<pre>
+---------+ +---------------+
| | | |
| |&gt;--(A)- Client Authentication ---&gt;| Authorization |
| Client | | Server |
| |&lt;--(B)---- Access Token ---------&lt;| |
| | | |
+---------+ +---------------+</pre>
</figure>
<p>
The flow illustrated in <a href="#figure-6">Client Credentials Flow</a> includes the following steps:
</p>
<ol class="alpha">
<li> <p>
The client authenticates with the authorization server and requests an access token
from the token endpoint.
</p>
</li>
<li> <p>
The authorization server authenticates the client, and if valid issues an access
token.
</p>
</li>
</ol>
<section id="authorization-request-and-response">
<h4>Authorization Request and Response</h4>
<p>
Since the client authentication is used as the authorization grant, no additional
authorization request is needed.
</p>
</section>
<section id="client-req">
<h4>Access Token Request</h4>
<p>
The client makes a request to the token endpoint by adding the following parameters
using the application/x-www-form-urlencoded format
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a> with a character encoding of UTF-8
in the HTTP request entity-body:
</p>
<dl>
<dt>grant_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to client_credentials.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL. The scope of the access request as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
</dl>
<p>
The client MUST authenticate with the authorization server as described in
<a href="#token-endpoint-auth">Client Authentication</a>.
</p>
<figure>
<p class="preamble">
For example, the client makes the following HTTP request using transport-layer
security (with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials</pre>
</figure>
<p>
The authorization server MUST authenticate the client.
</p>
</section>
<section id="access-token-response">
<h4>Access Token Response</h4>
<p>
If the access token request is valid and authorized, the authorization server issues an
access token as described in <a href="#token-response">Successful Response</a>. A refresh token SHOULD
NOT be included. If the request failed client authentication or is invalid, the
authorization server returns an error response as described in
<a href="#token-errors">Error Response</a>.
</p>
<figure>
<p class="preamble">
An example successful response:
</p>
<pre>
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
&quot;access_token&quot;:&quot;2YotnFZFEjr1zCsicMWpAA&quot;,
&quot;token_type&quot;:&quot;example&quot;,
&quot;expires_in&quot;:3600,
&quot;example_parameter&quot;:&quot;example_value&quot;
}</pre>
</figure>
</section>
</section>
<section id="ext-grant">
<h3>Extension Grants</h3>
<p>
The client uses an extension grant type by specifying the grant type using an
absolute URI (defined by the authorization server) as the value of the
grant_type parameter of the token endpoint, and by
adding any additional parameters necessary.
</p>
<figure>
<p class="preamble">
For example, to request an access token using a SAML 2.0 assertion grant type as
defined by <a href="#i-d-ietf-oauth-saml2-bearer">I-D.ietf-oauth-saml2-bearer</a>, the client could make the
following HTTP request using TLS (with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Asaml2-
bearer&amp;assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ9IjIwMTEtMDU
[...omitted for brevity...]aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-</pre>
</figure>
<p>
If the access token request is valid and authorized, the authorization server issues an
access token and optional refresh token as described in <a href="#token-response">Successful Response</a>.
If the request failed client authentication or is invalid, the authorization server returns
an error response as described in <a href="#token-errors">Error Response</a>.
</p>
</section>
</section>
<section id="token-issue">
<h2>Issuing an Access Token</h2>
<p>
If the access token request is valid and authorized, the authorization server issues an
access token and optional refresh token as described in <a href="#token-response">Successful Response</a>.
If the request failed client authentication or is invalid, the authorization server returns
an error response as described in <a href="#token-errors">Error Response</a>.
</p>
<section id="token-response">
<h3>Successful Response</h3>
<p>
The authorization server issues an access token and optional refresh token, and
constructs the response by adding the following parameters to the entity body of the HTTP
response with a 200 (OK) status code:
</p>
<dl>
<dt>access_token</dt>
<dd> <p>
REQUIRED. The access token issued by the authorization server.
</p>
</dd>
<dt>token_type</dt>
<dd> <p>
REQUIRED. The type of the token issued as described in <a href="#token-types">Access Token Types</a>.
Value is case insensitive.
</p>
</dd>
<dt>expires_in</dt>
<dd> <p>
RECOMMENDED. The lifetime in seconds of the access token. For example, the value
3600 denotes that the access token will expire in one
hour from the time the response was generated. If omitted, the authorization server
SHOULD provide the expiration time via other means or document the default value.
</p>
</dd>
<dt>refresh_token</dt>
<dd> <p>
OPTIONAL. The refresh token, which can be used to obtain new access tokens using the
same authorization grant as described in <a href="#token-refresh">Refreshing an Access Token</a>.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL, if identical to the scope requested by the client, otherwise REQUIRED. The
scope of the access token as described by <a href="#scope">Access Token Scope</a>.
</p>
</dd>
</dl>
<p>
The parameters are included in the entity body of the HTTP response using the
application/json media type as defined by
<a href="#rfc4627">RFC4627</a>. The parameters are serialized into a JSON structure by
adding each parameter at the highest structure level. Parameter names and string values
are included as JSON strings. Numerical values are included as JSON numbers. The order of
parameters does not matter and can vary.
</p>
<p>
The authorization server MUST include the HTTP
Cache-Control response header field <a href="#rfc2616">RFC2616</a>
with a value of no-store in any response containing tokens,
credentials, or other sensitive information, as well as the
Pragma response header field <a href="#rfc2616">RFC2616</a> with a
value of no-cache.
</p>
<figure>
<p class="preamble">
For example:
</p>
<pre>
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
&quot;access_token&quot;:&quot;2YotnFZFEjr1zCsicMWpAA&quot;,
&quot;token_type&quot;:&quot;example&quot;,
&quot;expires_in&quot;:3600,
&quot;refresh_token&quot;:&quot;tGzv3JOkF0XG5Qx2TlKWIA&quot;,
&quot;example_parameter&quot;:&quot;example_value&quot;
}</pre>
</figure>
<p>
The client MUST ignore unrecognized value names in the response. The sizes of tokens and
other values received from the authorization server are left undefined. The client should
avoid making assumptions about value sizes. The authorization server SHOULD document the
size of any value it issues.
</p>
</section>
<section id="token-errors">
<h3>Error Response</h3>
<p>
The authorization server responds with an HTTP 400 (Bad Request) status code (unless
specified otherwise) and includes the following parameters with the response:
</p>
<dl>
<dt>error</dt>
<dd> <p>
REQUIRED. A single ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> error code from the following:
</p>
<dl>
<dt>invalid_request</dt>
<dd> <p>
The request is missing a required parameter, includes an unsupported
parameter value (other than grant type), repeats a parameter, includes multiple
credentials, utilizes more than one mechanism for authenticating the client,
or is otherwise malformed.
</p>
</dd>
<dt>invalid_client</dt>
<dd> <p>
Client authentication failed (e.g. unknown client, no client authentication
included, or unsupported authentication method). The authorization server MAY
return an HTTP 401 (Unauthorized) status code to indicate which HTTP
authentication schemes are supported. If the client attempted to authenticate via
the Authorization request header field,
the authorization server MUST respond with an HTTP 401 (Unauthorized) status
code, and include the WWW-Authenticate response
header field matching the authentication scheme used by the client.
</p>
</dd>
<dt>invalid_grant</dt>
<dd> <p>
The provided authorization grant (e.g. authorization code, resource owner
credentials) or refresh token is invalid, expired, revoked, does not match the
redirection URI used in the authorization request, or was issued to another
client.
</p>
</dd>
<dt>unauthorized_client</dt>
<dd> <p>
The authenticated client is not authorized to use this authorization grant type.
</p>
</dd>
<dt>unsupported_grant_type</dt>
<dd> <p>
The authorization grant type is not supported by the authorization server.
</p>
</dd>
<dt>invalid_scope</dt>
<dd> <p>
The requested scope is invalid, unknown, malformed, or exceeds the scope granted
by the resource owner.
</p>
</dd>
</dl>
<p>
Values for the error parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_description</dt>
<dd> <p>
OPTIONAL. A human-readable ASCII <a href="#usascii">Coded Character Set -- 7-bit American Standard Code for Information Interchange</a> text providing additional information,
used to assist the client developer in understanding the error that occurred.
Values for the error_description parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>error_uri</dt>
<dd> <p>
OPTIONAL. A URI identifying a human-readable web page with information about the
error, used to provide the client developer with additional information about the
error.
Values for the error_uri parameter
MUST conform to the URI-Reference syntax, and thus MUST NOT include
characters outside the set %x21 / %x23-5B / %x5D-7E.
</p>
</dd>
</dl>
<p>
The parameters are included in the entity body of the HTTP response using the
application/json media type as defined by
<a href="#rfc4627">RFC4627</a>. The parameters are serialized into a JSON structure by
adding each parameter at the highest structure level. Parameter names and string values
are included as JSON strings. Numerical values are included as JSON numbers. The order of
parameters does not matter and can vary.
</p>
<figure>
<p class="preamble">
For example:
</p>
<pre>
HTTP/1.1 400 Bad Request
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
&quot;error&quot;:&quot;invalid_request&quot;
}</pre>
</figure>
</section>
</section>
<section id="token-refresh">
<h2>Refreshing an Access Token</h2>
<p>
If the authorization server issued a refresh token to the client, the client makes a
refresh request to the token endpoint by adding the following parameters using the
application/x-www-form-urlencoded format
per <a href="#urlencoded">Use of application/x-www-form-urlencoded Media Type</a> with a character encoding of UTF-8
in the HTTP request entity-body:
</p>
<dl>
<dt>grant_type</dt>
<dd> <p>
REQUIRED. Value MUST be set to refresh_token.
</p>
</dd>
<dt>refresh_token</dt>
<dd> <p>
REQUIRED. The refresh token issued to the client.
</p>
</dd>
<dt>scope</dt>
<dd> <p>
OPTIONAL. The scope of the access request as described by <a href="#scope">Access Token Scope</a>.
The requested scope MUST NOT include any scope not originally granted by the resource
owner, and if omitted is treated as equal to the scope originally granted by the
resource owner.
</p>
</dd>
</dl>
<p>
Because refresh tokens are typically long-lasting credentials used to request additional
access tokens, the refresh token is bound to the client to which it was issued. If the client type
is confidential or the client was issued client credentials (or assigned other
authentication requirements), the client MUST authenticate with the authorization server as
described in <a href="#token-endpoint-auth">Client Authentication</a>.
</p>
<figure>
<p class="preamble">
For example, the client makes the following HTTP request using transport-layer
security (with extra line breaks for display purposes only):
</p>
<pre>
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&amp;refresh_token=tGzv3JOkF0XG5Qx2TlKWIA</pre>
</figure>
<p>
The authorization server MUST:
</p>
<ul class="symbols">
<li> <p>
require client authentication for confidential clients or for any client that was
issued client credentials (or with other authentication requirements),
</p>
</li>
<li> <p>
authenticate the client if client authentication is included and ensure the
refresh token was issued to the authenticated client, and
</p>
</li>
<li> <p>
validate the refresh token.
</p>
</li>
</ul>
<p>
If valid and authorized, the authorization server issues an access token as described in
<a href="#token-response">Successful Response</a>. If the request failed verification or is invalid, the
authorization server returns an error response as described in
<a href="#token-errors">Error Response</a>.
</p>
<p>
The authorization server MAY issue a new refresh token, in which case the client MUST
discard the old refresh token and replace it with the new refresh token. The authorization
server MAY revoke the old refresh token after issuing a new refresh token to the client. If
a new refresh token is issued, the refresh token scope MUST be identical to that of the
refresh token included by the client in the request.
</p>
</section>
<section id="access-resource">
<h2>Accessing Protected Resources</h2>
<p>
The client accesses protected resources by presenting the access token to the resource
server. The resource server MUST validate the access token and ensure it has not expired
and that its scope covers the requested resource. The methods used by the resource server
to validate the access token (as well as any error responses) are beyond the scope of this
specification, but generally involve an interaction or coordination between the resource
server and the authorization server.
</p>
<p>
The method in which the client utilizes the access token to authenticate with the resource
server depends on the type of access token issued by the authorization server. Typically,
it involves using the HTTP Authorization request header field
<a href="#rfc2617">RFC2617</a> with an authentication scheme defined by the access token type
specification.
</p>
<section id="token-types">
<h3>Access Token Types</h3>
<p>
The access token type provides the client with the information required to successfully
utilize the access token to make a protected resource request (along with type-specific
attributes). The client MUST NOT use an access token if it does not understand the token
type.
</p>
<figure>
<p class="preamble">
For example, the bearer token type defined in
<a href="#i-d-ietf-oauth-v2-bearer">I-D.ietf-oauth-v2-bearer</a> is utilized by simply including the access
token string in the request:
</p>
<pre>
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Bearer mF_9.B5f-4.1JqM</pre>
</figure>
<figure>
<p class="preamble">
while the mac token type defined in
<a href="#i-d-ietf-oauth-v2-http-mac">I-D.ietf-oauth-v2-http-mac</a> is utilized by issuing a MAC key
together with the access token that is used to sign certain components of the HTTP
requests:
</p>
<pre>
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: MAC id=&quot;h480djs93hd8&quot;,
nonce=&quot;274312:dj83hs9s&quot;,
mac=&quot;kDZvddkndxvhGRXZhvuDjEWhGeE=&quot;</pre>
</figure>
<p>
The above examples are provided for illustration purposes only. Developers are advised to
consult the <a href="#i-d-ietf-oauth-v2-bearer">I-D.ietf-oauth-v2-bearer</a> and
<a href="#i-d-ietf-oauth-v2-http-mac">I-D.ietf-oauth-v2-http-mac</a> specifications before use.
</p>
<p>
Each access token type definition specifies the additional attributes (if any) sent to
the client together with the access_token response parameter.
It also defines the HTTP authentication method used to include the access token when
making a protected resource request.
</p>
</section>
<section id="resource-errors">
<h3>Error Response</h3>
<p>
If a resource access request fails, the resource server SHOULD inform
the client of the error. While the specifics of such error responses
are beyond the scope of this specification, this documents establishes
a common registry in <a href="#error-registry">OAuth Extensions Error Registry</a> for error values
to be shared among OAuth token authentication schemes.
</p>
<p>
New authentication schemes designed primarily for OAuth token
authentication SHOULD define a mechanism for providing an
error status code to the client, in which the error values allowed are
registered in the error registry established by this specification. Such
schemes MAY limit the set of valid error codes to a subset of the
registered values. If the error code is returned using a named parameter,
the parameter name SHOULD be error.
</p>
<p>
Other schemes capable of being used for OAuth token authentication, but
not primarily designed for that purpose, MAY bind their error values to the
registry in the same manner.
</p>
<p>
New authentication schemes MAY choose to also specify the use of the
error_description and
error_uri
parameters to return error information in a manner parallel
to their usage in this specification.
</p>
</section>
</section>
<section id="extensions">
<h2>Extensibility</h2>
<section id="new-types">
<h3>Defining Access Token Types</h3>
<p>
Access token types can be defined in one of two ways: registered in the access token type
registry (following the procedures in <a href="#type-registry">OAuth Access Token Type Registry</a>), or by using a
unique absolute URI as its name.
</p>
<p>
Types utilizing a URI name SHOULD be limited to vendor-specific implementations that are
not commonly applicable, and are specific to the implementation details of the resource
server where they are used.
</p>
<p>
All other types MUST be registered. Type names MUST conform to the type-name ABNF. If the
type definition includes a new HTTP authentication scheme, the type name SHOULD be
identical to the HTTP authentication scheme name (as defined by <a href="#rfc2617">RFC2617</a>).
The token type example is reserved for use in examples.
</p>
<figure>
<pre>
type-name = 1*name-char
name-char = &quot;-&quot; / &quot;.&quot; / &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
</section>
<section id="endpoint-params">
<h3>Defining New Endpoint Parameters</h3>
<p>
New request or response parameters for use with the authorization endpoint or the token
endpoint are defined and registered in the parameters registry following the procedure in
<a href="#parameters-registry">OAuth Parameters Registry</a>.
</p>
<p>
Parameter names MUST conform to the param-name ABNF and parameter values syntax MUST be
well-defined (e.g., using ABNF, or a reference to the syntax of an existing parameter).
</p>
<figure>
<pre>
param-name = 1*name-char
name-char = &quot;-&quot; / &quot;.&quot; / &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
<p>
Unregistered vendor-specific parameter extensions that are not commonly applicable, and
are specific to the implementation details of the authorization server where they are
used SHOULD utilize a vendor-specific prefix that is not likely to conflict with other
registered values (e.g. begin with 'companyname_').
</p>
</section>
<section id="defining-new-authorization-grant-types">
<h3>Defining New Authorization Grant Types</h3>
<p>
New authorization grant types can be defined by assigning them a unique absolute URI for
use with the grant_type parameter. If the extension grant
type requires additional token endpoint parameters, they MUST be registered in the OAuth
parameters registry as described by <a href="#parameters-registry">OAuth Parameters Registry</a>.
</p>
</section>
<section id="response-type-ext">
<h3>Defining New Authorization Endpoint Response Types</h3>
<p>
New response types for use with the authorization endpoint are defined and registered in
the authorization endpoint response type registry following the procedure in
<a href="#response-type-registry">OAuth Authorization Endpoint Response Type Registry</a>. Response type names MUST conform to the
response-type ABNF.
</p>
<figure>
<pre>
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
<p>
If a response type contains one or more space characters (%x20), it is compared as a
space-delimited list of values in which the order of values does not matter. Only one
order of values can be registered, which covers all other arrangements of the same set of
values.
</p>
<p>
For example, the response type token code is left undefined
by this specification. However, an extension can define and register the
token code response type. Once registered, the same
combination cannot be registered as code token, but both
values can be used to denote the same response type.
</p>
</section>
<section id="new-errors">
<h3>Defining Additional Error Codes</h3>
<p>
In cases where protocol extensions (i.e. access token types, extension parameters, or
extension grant types) require additional error codes to be used with the authorization
code grant error response (<a href="#code-authz-error">Error Response</a>), the implicit grant error
response (<a href="#implicit-authz-error">Error Response</a>), the token error response
(<a href="#token-errors">Error Response</a>),
or the resource access error response (<a href="#resource-errors">Error Response</a>),
such error codes MAY be defined.
</p>
<p>
Extension error codes MUST be registered (following the procedures in
<a href="#error-registry">OAuth Extensions Error Registry</a>) if the extension they are used in conjunction with is
a registered access token type, a registered endpoint parameter, or an extension grant
type. Error codes used with unregistered extensions MAY be registered.
</p>
<p>
Error codes MUST conform to the error ABNF, and SHOULD be prefixed by an identifying
name when possible. For example, an error identifying an invalid value set to the
extension parameter example SHOULD be named
example_invalid.
</p>
<figure>
<pre>
error = 1*error-char
error-char = %x20-21 / %x23-5B / %x5D-7E</pre>
</figure>
</section>
</section>
<section id="NativeApps">
<h2>Native Applications</h2>
<p>
Native applications are clients installed and executed on the device used by the resource
owner (i.e. desktop application, native mobile application). Native applications require
special consideration related to security, platform capabilities, and overall end-user
experience.
</p>
<p>
The authorization endpoint requires interaction between the client and the resource
owner's user-agent. Native applications can invoke an external user-agent or embed a
user-agent within the application. For example:
</p>
<ul class="symbols">
<li> <p>
External user-agent - the native application can capture the response from the
authorization server using a redirection URI with a scheme registered with the
operating system to invoke the client as the handler, manual copy-and-paste of the
credentials, running a local web server, installing a user-agent extension, or by
providing a redirection URI identifying a server-hosted resource under the client's
control, which in turn makes the response available to the native application.
</p>
</li>
<li> <p>
Embedded user-agent - the native application obtains the response by directly
communicating with the embedded user-agent by monitoring state changes emitted during
the resource load, or accessing the user-agent's cookies storage.
</p>
</li>
</ul>
<p>
When choosing between an external or embedded user-agent, developers should consider:
</p>
<ul class="symbols">
<li> <p>
An External user-agent may improve completion rate as the resource owner may already have
an active session with the authorization server removing the need to re-authenticate. It
provides a familiar end-user experience and functionality. The resource owner may also
rely on user-agent features or extensions to assist with authentication (e.g. password
manager, 2-factor device reader).
</p>
</li>
<li> <p>
An embedded user-agent may offer improved usability, as it removes the need to switch
context and open new windows.
</p>
</li>
<li> <p>
An embedded user-agent poses a security challenge because resource owners are
authenticating in an unidentified window without access to the visual protections found
in most external user-agents. An embedded user-agent educates end-users to trust
unidentified requests for authentication (making phishing attacks easier to execute).
</p>
</li>
</ul>
<p>
When choosing between the implicit grant type and the authorization code grant type, the
following should be considered:
</p>
<ul class="symbols">
<li> <p>
Native applications that use the authorization code grant type SHOULD do so without
using client credentials, due to the native application's inability to keep client
credentials confidential.
</p>
</li>
<li> <p>
When using the implicit grant type flow, a refresh token is not returned, which requires
repeating the authorization process once the access token expires.
</p>
</li>
</ul>
</section>
<section id="security-considerations">
<h2>Security Considerations</h2>
<p>
As a flexible and extensible framework, OAuth's security considerations depend on many
factors. The following sections provide implementers with security guidelines focused on
the three client profiles described in <a href="#client-types">Client Types</a>: web application,
user-agent-based application, and native application.
</p>
<p>
A comprehensive OAuth security model and analysis, as well as background for the protocol
design, is provided by <a href="#i-d-ietf-oauth-v2-threatmodel">I-D.ietf-oauth-v2-threatmodel</a>.
</p>
<section id="client-authentication">
<h3>Client Authentication</h3>
<p>
The authorization server establishes client credentials with web application clients for
the purpose of client authentication. The authorization server is encouraged to consider
stronger client authentication means than a client password. Web application clients MUST
ensure confidentiality of client passwords and other client credentials.
</p>
<p>
The authorization server MUST NOT issue client passwords or other client credentials to
native application or user-agent-based application clients for the purpose of client
authentication. The authorization server MAY issue a client password or other credentials
for a specific installation of a native application client on a specific device.
</p>
<p>
When client authentication is not possible, the authorization server SHOULD employ other
means to validate the client's identity. For example, by requiring the registration of
the client redirection URI or enlisting the resource owner to confirm identity. A valid
redirection URI is not sufficient to verify the client's identity when asking for
resource owner authorization, but can be used to prevent delivering credentials to a
counterfeit client after obtaining resource owner authorization.
</p>
<p>
The authorization server must consider the security implications of interacting with
unauthenticated clients and take measures to limit the potential exposure of other
credentials (e.g. refresh tokens) issued to such clients.
</p>
</section>
<section id="client-impersonation">
<h3>Client Impersonation</h3>
<p>
A malicious client can impersonate another client and obtain access to protected
resources, if the impersonated client fails to, or is unable to, keep its client
credentials confidential.
</p>
<p>
The authorization server MUST authenticate the client whenever possible. If the
authorization server cannot authenticate the client due to the client's nature, the
authorization server MUST require the registration of any redirection URI used for
receiving authorization responses, and SHOULD utilize other means to protect resource
owners from such potentially malicious clients. For example, the authorization server
can engage the resource owner to assist in identifying the client and its origin.
</p>
<p>
The authorization server SHOULD enforce explicit resource owner authentication and
provide the resource owner with information about the client and the requested
authorization scope and lifetime. It is up to the resource owner to review the
information in the context of the current client, and authorize or deny the request.
</p>
<p>
The authorization server SHOULD NOT process repeated authorization requests
automatically (without active resource owner interaction) without authenticating the
client or relying on other measures to ensure the repeated request comes from the
original client and not an impersonator.
</p>
</section>
<section id="AccessTokenSecurity">
<h3>Access Tokens</h3>
<p>
Access token credentials (as well as any confidential access token attributes) MUST be
kept confidential in transit and storage, and only shared among the authorization server,
the resource servers the access token is valid for, and the client to whom the access
token is issued. Access token credentials MUST only be transmitted using TLS as described
in <a href="#tls">TLS Version</a> with server authentication as defined by
<a href="#rfc2818">RFC2818</a>.
</p>
<p>
When using the implicit grant type, the access token is transmitted in the URI fragment,
which can expose it to unauthorized parties.
</p>
<p>
The authorization server MUST ensure that access tokens cannot be generated, modified, or
guessed to produce valid access tokens by unauthorized parties.
</p>
<p>
The client SHOULD request access tokens with the minimal scope necessary. The
authorization server SHOULD take the client identity into account when choosing how
to honor the requested scope, and MAY issue an access token with a less rights than
requested.
</p>
<p>
This specification does not provide any methods for the resource server to ensure that an
access token presented to it by a given client was issued to that client by the
authorization server.
</p>
</section>
<section id="refresh-tokens">
<h3>Refresh Tokens</h3>
<p>
Authorization servers MAY issue refresh tokens to web application clients and native
application clients.
</p>
<p>
Refresh tokens MUST be kept confidential in transit and storage, and shared only among
the authorization server and the client to whom the refresh tokens were issued. The
authorization server MUST maintain the binding between a refresh token and the client to
whom it was issued. Refresh tokens MUST only be transmitted using TLS as described in
<a href="#tls">TLS Version</a> with server authentication as defined by <a href="#rfc2818">RFC2818</a>.
</p>
<p>
The authorization server MUST verify the binding between the refresh token and client
identity whenever the client identity can be authenticated. When client authentication is
not possible, the authorization server SHOULD deploy other means to detect refresh token
abuse.
</p>
<p>
For example, the authorization server could employ refresh token rotation in which a new
refresh token is issued with every access token refresh response. The previous refresh
token is invalidated but retained by the authorization server. If a refresh token is
compromised and subsequently used by both the attacker and the legitimate client, one of
them will present an invalidated refresh token, which will inform the authorization server
of the breach.
</p>
<p>
The authorization server MUST ensure that refresh tokens cannot be generated, modified,
or guessed to produce valid refresh tokens by unauthorized parties.
</p>
</section>
<section id="authorization-codes">
<h3>Authorization Codes</h3>
<p>
The transmission of authorization codes SHOULD be made over a secure channel, and the
client SHOULD require the use of TLS with its redirection URI if the URI identifies a
network resource. Since authorization codes are transmitted via user-agent redirections,
they could potentially be disclosed through user-agent history and HTTP referrer headers.
</p>
<p>
Authorization codes operate as plaintext bearer credentials, used to verify that the
resource owner who granted authorization at the authorization server is the same
resource owner returning to the client to complete the process. Therefore, if the client
relies on the authorization code for its own resource owner authentication, the client
redirection endpoint MUST require the use of TLS.
</p>
<p>
Authorization codes MUST be short lived and single use. If the authorization server
observes multiple attempts to exchange an authorization code for an access token, the
authorization server SHOULD attempt to revoke all access tokens already granted based on
the compromised authorization code.
</p>
<p>
If the client can be authenticated, the authorization servers MUST authenticate the
client and ensure that the authorization code was issued to the same client.
</p>
</section>
<section id="authorization-code-redirection-uri-manipulation">
<h3>Authorization Code Redirection URI Manipulation</h3>
<p>
When requesting authorization using the authorization code grant type, the client can
specify a redirection URI via the redirect_uri parameter.
If an attacker can manipulate the value of the redirection URI, it can cause the
authorization server to redirect the resource owner user-agent to a URI under the control
of the attacker with the authorization code.
</p>
<p>
An attacker can create an account at a legitimate client and initiate the authorization
flow. When the attacker's user-agent is sent to the authorization server to grant access,
the attacker grabs the authorization URI provided by the legitimate client, and replaces
the client's redirection URI with a URI under the control of the attacker. The attacker
then tricks the victim into following the manipulated link to authorize access to the
legitimate client.
</p>
<p>
Once at the authorization server, the victim is prompted with a normal, valid request on
behalf of a legitimate and trusted client, and authorizes the request. The victim is
then redirected to an endpoint under the control of the attacker with the authorization
code. The attacker completes the authorization flow by sending the authorization code to
the client using the original redirection URI provided by the client. The client
exchanges the authorization code with an access token and links it to the attacker's
client account, which can now gain access to the protected resources authorized by the
victim (via the client).
</p>
<p>
In order to prevent such an attack, the authorization server MUST ensure that the
redirection URI used to obtain the authorization code is identical to the redirection URI
provided when exchanging the authorization code for an access token. The authorization
server MUST require public clients and SHOULD require confidential clients to register
their redirection URIs. If a redirection URI is provided in the request, the
authorization server MUST validate it against the registered value.
</p>
</section>
<section id="resource-owner-password-credentials">
<h3>Resource Owner Password Credentials</h3>
<p>
The resource owner password credentials grant type is often used for legacy or migration
reasons. It reduces the overall risk of storing username and password by the client, but
does not eliminate the need to expose highly privileged credentials to the client.
</p>
<p>
This grant type carries a higher risk than other grant types because it maintains the
password anti-pattern this protocol seeks to avoid. The client could abuse the password
or the password could unintentionally be disclosed to an attacker (e.g. via log files or
other records kept by the client).
</p>
<p>
Additionally, because the resource owner does not have control over the authorization
process (the resource owner involvement ends when it hands over its credentials to the
client), the client can obtain access tokens with a broader scope than desired by the
resource owner. The authorization server should consider the scope and lifetime of
access tokens issued via this grant type.
</p>
<p>
The authorization server and client SHOULD minimize use of this grant type and utilize
other grant types whenever possible.
</p>
</section>
<section id="request-confidentiality">
<h3>Request Confidentiality</h3>
<p>
Access tokens, refresh tokens, resource owner passwords, and client credentials MUST NOT
be transmitted in the clear. Authorization codes SHOULD NOT be transmitted in the clear.
</p>
<p>
The state and scope parameters
SHOULD NOT include sensitive client or resource owner information in plain text as they
can be transmitted over insecure channels or stored insecurely.
</p>
</section>
<section id="endpoints-authenticity">
<h3>Endpoints Authenticity</h3>
<p>
In order to prevent man-in-the-middle attacks, the authorization server MUST require the
use of TLS with server authentication as defined by <a href="#rfc2818">RFC2818</a> for
any request sent to the authorization and token endpoints. The client MUST validate the
authorization server's TLS certificate as defined by <a href="#rfc6125">RFC6125</a>, and in
accordance with its requirements for server identity authentication.
</p>
</section>
<section id="anthropy">
<h3>Credentials Guessing Attacks</h3>
<p>
The authorization server MUST prevent attackers from guessing access tokens,
authorization codes, refresh tokens, resource owner passwords, and client credentials.
</p>
<p>
The probability of an attacker guessing generated tokens (and other credentials not
intended for handling by end-users) MUST be less than or equal to 2^(-128) and SHOULD be
less than or equal to 2^(-160).
</p>
<p>
The authorization server MUST utilize other means to protect credentials intended for
end-user usage.
</p>
</section>
<section id="phishing-attacks">
<h3>Phishing Attacks</h3>
<p>
Wide deployment of this and similar protocols may cause end-users to become inured
to the practice of being redirected to websites where they are asked to enter their
passwords. If end-users are not careful to verify the authenticity of these websites
before entering their credentials, it will be possible for attackers to exploit this
practice to steal resource owners' passwords.
</p>
<p>
Service providers should attempt to educate end-users about the risks phishing attacks
pose, and should provide mechanisms that make it easy for end-users to confirm the
authenticity of their sites. Client developers should consider the security implications
of how they interact with the user-agent (e.g., external, embedded), and the ability of
the end-user to verify the authenticity of the authorization server.
</p>
<p>
To reduce the risk of phishing attacks, the authorization servers MUST require the use of
TLS on every endpoint used for end-user interaction.
</p>
</section>
<section id="CSRF">
<h3>Cross-Site Request Forgery</h3>
<p>
Cross-site request forgery (CSRF) is an exploit in which an attacker causes the
user-agent of a victim end-user to follow a malicious URI (e.g. provided to the
user-agent as a misleading link, image, or redirection) to a trusting server (usually
established via the presence of a valid session cookie).
</p>
<p>
A CSRF attack against the client's redirection URI allows an attacker to inject their own
authorization code or access token, which can result in the client using an access token
associated with the attacker's protected resources rather than the victim's (e.g. save
the victim's bank account information to a protected resource controlled by the
attacker).
</p>
<p>
The client MUST implement CSRF protection for its redirection URI. This is typically
accomplished by requiring any request sent to the redirection URI endpoint to include a
value that binds the request to the user-agent's authenticated state (e.g. a hash of the
session cookie used to authenticate the user-agent). The client SHOULD utilize the
state request parameter to deliver this value to the
authorization server when making an authorization request.
</p>
<p>
Once authorization has been obtained from the end-user, the authorization server
redirects the end-user's user-agent back to the client with the required binding value
contained in the state parameter. The binding value enables
the client to verify the validity of the request by matching the binding value to the
user-agent's authenticated state. The binding value used for CSRF protection MUST contain
a non-guessable value (as described in <a href="#anthropy">Credentials Guessing Attacks</a>), and the user-agent's
authenticated state (e.g. session cookie, HTML5 local storage) MUST be kept in a location
accessible only to the client and the user-agent (i.e., protected by same-origin policy).
</p>
<p>
A CSRF attack against the authorization server's authorization endpoint can result in an
attacker obtaining end-user authorization for a malicious client without involving or
alerting the end-user.
</p>
<p>
The authorization server MUST implement CSRF protection for its authorization endpoint,
and ensure that a malicious client cannot obtain authorization without the awareness and
explicit consent of the resource owner.
</p>
</section>
<section id="clickjacking">
<h3>Clickjacking</h3>
<p>
In a clickjacking attack, an attacker registers a legitimate client and then constructs a
malicious site in which it loads the authorization server's authorization endpoint web
page in a transparent iframe overlaid on top of a set of dummy buttons, which are
carefully constructed to be placed directly under important buttons on the authorization
page. When an end-user clicks a misleading visible button, the end-user is actually
clicking an invisible button on the authorization page (such as an &quot;Authorize&quot; button).
This allows an attacker to trick a resource owner into granting its client access without
their knowledge.
</p>
<p>
To prevent this form of attack, native applications SHOULD use external browsers instead
of embedding browsers within the application when requesting end-user authorization. For
most newer browsers, avoidance of iframes can be enforced by the authorization server
using the (non-standard) x-frame-options header. This header
can have two values, deny and
sameorigin, which will block any framing, or framing by sites
with a different origin, respectively. For older browsers, JavaScript framebusting
techniques can be used but may not be effective in all browsers.
</p>
</section>
<section id="code-injection-and-input-validation">
<h3>Code Injection and Input Validation</h3>
<p>
A code injection attack occurs when an input or otherwise external variable is used by an
application unsanitized and causes modification to the application logic. This may allow
an attacker to gain access to the application device or its data, cause denial of
service, or a wide range of malicious side-effects.
</p>
<p>
The Authorization server and client MUST sanitize (and validate when possible) any value
received, in particular, the value of the state and
redirect_uri parameters.
</p>
</section>
<section id="open-redirect">
<h3>Open Redirectors</h3>
<p>
The authorization server authorization endpoint and the client redirection endpoint can
be improperly configured and operate as open redirectors. An open redirector is an
endpoint using a parameter to automatically redirect a user-agent to the location
specified by the parameter value without any validation.
</p>
<p>
Open redirectors can be used in phishing attacks, or by an attacker to get end-users to
visit malicious sites by making the URI's authority look like a familiar and trusted
destination. In addition, if the authorization server allows the client to register only
part of the redirection URI, an attacker can use an open redirector operated by the
client to construct a redirection URI that will pass the authorization server validation
but will send the authorization code or access token to an endpoint under the control of
the attacker.
</p>
</section>
<section id="ImplicitImpersonation">
<h3>Misuse of Access Token to Impersonate Resource Owner in Implicit Flow</h3>
<p>
For public clients using implicit flows, this specification does not provide any
method for the client to determine what client an access token was issued to.
</p>
<p>
A Resource Owner may willingly delegate access to a resource by granting an access token
to an attacker's malicious client. This may be due to Phishing or some other pretext.
An attacker may also steal a token via some other mechanism.
An attacker may then attempt to impersonate the resource owner by providing the
access token to a legitimate public client.
</p>
<p>
In the implicit flow (response_type=token), the attacker can easily switch the token
in the response from the authorization server,
replacing the real access_token with the one previously issued to the attacker.
</p>
<p>
Servers communicating with native applications that rely on being passed
an access token in the back channel to identify the user of the client may
be similarly compromised by an attacker creating a compromised application
that can inject arbitrary stolen access tokens.
</p>
<p>
Any public client that makes the assumption that only the resource owner
can present them with a valid access token for the resource
is vulnerable to this attack.
</p>
<p>
This attack may expose information about the resource owner
at the legitimate client to the attacker (malicious client).
This will also allow the attacker to perform operations
at the legitimate client with the same permissions as the resource owner
who originally granted the access token or authorization code.
</p>
<p>
Authenticating Resource Owners to clients is out of scope for this specification.
Any specification that uses the authorization process as a form of
delegated end-user authentication to the client (e.g. third-party sign-in service)
MUST NOT use the implicit flow without additional security mechanisms
such as audience restricting the access token
that enable the client to determine if the access token was issued for its use.
</p>
</section>
</section>
<section id="iana-considerations">
<h2>IANA Considerations</h2>
<section id="type-registry">
<h3>OAuth Access Token Type Registry</h3>
<p>
This specification establishes the OAuth access token type registry.
</p>
<p>
Access token types are registered with a Specification Required
(<a href="#rfc5226">RFC5226</a>) after a two week review period on the [TBD]@ietf.org mailing
list, on the advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s) may approve
registration once they are satisfied that such a specification will be published.
</p>
<p>
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and
comment, with an appropriate subject (e.g., &quot;Request for access token type: example&quot;).
[[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation
with the IESG and IANA. Suggested name: oauth-ext-review. ]]
</p>
<p>
Within the review period, the Designated Expert(s) will either approve or
deny the registration request, communicating this decision to the review list and IANA.
Denials should include an explanation and, if applicable, suggestions as to how to make
the request successful.
</p>
<p>
IANA must only accept registry updates from the Designated Expert(s), and should direct
all requests for registration to the review mailing list.
</p>
<section id="registration-template">
<h4>Registration Template</h4>
<dl>
<dt>Type name:</dt>
<dd> <p>
The name requested (e.g., &quot;example&quot;).
</p>
</dd>
<dt>Additional Token Endpoint Response Parameters:</dt>
<dd> <p>
Additional response parameters returned together with the
access_token parameter. New parameters MUST be
separately registered in the OAuth parameters registry as described by
<a href="#parameters-registry">OAuth Parameters Registry</a>.
</p>
</dd>
<dt>HTTP Authentication Scheme(s):</dt>
<dd> <p>
The HTTP authentication scheme name(s), if any, used to authenticate protected
resources requests using access tokens of this type.
</p>
</dd>
<dt>Change controller:</dt>
<dd> <p>
For standards-track RFCs, state &quot;IETF&quot;. For others, give the name of the
responsible party. Other details (e.g., postal address, e-mail address, home page
URI) may also be included.
</p>
</dd>
<dt>Specification document(s):</dt>
<dd> <p>
Reference to the document that specifies the parameter, preferably including a URI that
can be used to retrieve a copy of the document. An indication of the relevant
sections may also be included, but is not required.
</p>
</dd>
</dl>
</section>
</section>
<section id="parameters-registry">
<h3>OAuth Parameters Registry</h3>
<p>
This specification establishes the OAuth parameters registry.
</p>
<p>
Additional parameters for inclusion in the authorization endpoint request, the
authorization endpoint response, the token endpoint request, or the token endpoint
response are registered with a Specification Required
(<a href="#rfc5226">RFC5226</a>) after a two week review period on the [TBD]@ietf.org mailing
list, on the advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s) may approve
registration once they are satisfied that such a specification will be published.
</p>
<p>
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and
comment, with an appropriate subject (e.g., &quot;Request for parameter: example&quot;).
[[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation
with the IESG and IANA. Suggested name: oauth-ext-review. ]]
</p>
<p>
Within the review period, the Designated Expert(s) will either approve or
deny the registration request, communicating this decision to the review list and IANA.
Denials should include an explanation and, if applicable, suggestions as to how to make
the request successful.
</p>
<p>
IANA must only accept registry updates from the Designated Expert(s), and should direct
all requests for registration to the review mailing list.
</p>
<section id="registration-template">
<h4>Registration Template</h4>
<dl>
<dt>Parameter name:</dt>
<dd> <p>
The name requested (e.g., &quot;example&quot;).
</p>
</dd>
<dt>Parameter usage location:</dt>
<dd> <p>
The location(s) where parameter can be used. The possible locations are:
authorization request, authorization response, token request, or token response.
</p>
</dd>
<dt>Change controller:</dt>
<dd> <p>
For standards-track RFCs, state &quot;IETF&quot;. For others, give the name of the
responsible party. Other details (e.g., postal address, e-mail address, home page
URI) may also be included.
</p>
</dd>
<dt>Specification document(s):</dt>
<dd> <p>
Reference to the document that specifies the parameter, preferably including a URI that
can be used to retrieve a copy of the document. An indication of the relevant
sections may also be included, but is not required.
</p>
</dd>
</dl>
</section>
<section id="initial-registry-contents">
<h4>Initial Registry Contents</h4>
<p>
The OAuth Parameters Registry's initial contents are:
</p>
<ul class="symbols">
<li> <p>
Parameter name: client_id
</p>
</li>
<li> <p>
Parameter usage location: authorization request, token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: client_secret
</p>
</li>
<li> <p>
Parameter usage location: token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: response_type
</p>
</li>
<li> <p>
Parameter usage location: authorization request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: redirect_uri
</p>
</li>
<li> <p>
Parameter usage location: authorization request, token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: scope
</p>
</li>
<li> <p>
Parameter usage location: authorization request, authorization response, token
request, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: state
</p>
</li>
<li> <p>
Parameter usage location: authorization request, authorization response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: code
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: error_description
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: error_uri
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: grant_type
</p>
</li>
<li> <p>
Parameter usage location: token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: access_token
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: token_type
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: expires_in
</p>
</li>
<li> <p>
Parameter usage location: authorization response, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: username
</p>
</li>
<li> <p>
Parameter usage location: token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: password
</p>
</li>
<li> <p>
Parameter usage location: token request
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Parameter name: refresh_token
</p>
</li>
<li> <p>
Parameter usage location: token request, token response
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
</section>
</section>
<section id="response-type-registry">
<h3>OAuth Authorization Endpoint Response Type Registry</h3>
<p>
This specification establishes the OAuth authorization endpoint response type registry.
</p>
<p>
Additional response type for use with the authorization endpoint are registered with a
Specification Required (<a href="#rfc5226">RFC5226</a>) after a two week review period on
the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts.
However, to allow for the allocation of values prior to publication, the Designated
Expert(s) may approve registration once they are satisfied that such a specification
will be published.
</p>
<p>
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and
comment, with an appropriate subject (e.g., &quot;Request for response type: example&quot;).
[[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation
with the IESG and IANA. Suggested name: oauth-ext-review. ]]
</p>
<p>
Within the review period, the Designated Expert(s) will either approve or
deny the registration request, communicating this decision to the review list and IANA.
Denials should include an explanation and, if applicable, suggestions as to how to make
the request successful.
</p>
<p>
IANA must only accept registry updates from the Designated Expert(s), and should direct
all requests for registration to the review mailing list.
</p>
<section id="registration-template">
<h4>Registration Template</h4>
<dl>
<dt>Response type name:</dt>
<dd> <p>
The name requested (e.g., &quot;example&quot;).
</p>
</dd>
<dt>Change controller:</dt>
<dd> <p>
For standards-track RFCs, state &quot;IETF&quot;. For others, give the name of the
responsible party. Other details (e.g., postal address, e-mail address, home page
URI) may also be included.
</p>
</dd>
<dt>Specification document(s):</dt>
<dd> <p>
Reference to the document that specifies the type, preferably including a URI that
can be used to retrieve a copy of the document. An indication of the relevant
sections may also be included, but is not required.
</p>
</dd>
</dl>
</section>
<section id="initial-registry-contents">
<h4>Initial Registry Contents</h4>
<p>
The OAuth Authorization Endpoint Response Type Registry's initial contents are:
</p>
<ul class="symbols">
<li> <p>
Response type name: code
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
<ul class="symbols">
<li> <p>
Response type name: token
</p>
</li>
<li> <p>
Change controller: IETF
</p>
</li>
<li> <p>
Specification document(s): [[ this document ]]
</p>
</li>
</ul>
</section>
</section>
<section id="error-registry">
<h3>OAuth Extensions Error Registry</h3>
<p>
This specification establishes the OAuth extensions error registry.
</p>
<p>
Additional error codes used together with other protocol extensions (i.e. extension grant
types, access token types, or extension parameters) are registered with a Specification
Required (<a href="#rfc5226">RFC5226</a>) after a two week review period on the
[TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to
allow for the allocation of values prior to publication, the Designated Expert(s) may
approve registration once they are satisfied that such a specification will be published.
</p>
<p>
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and
comment, with an appropriate subject (e.g., &quot;Request for error code: example&quot;).
[[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation
with the IESG and IANA. Suggested name: oauth-ext-review. ]]
</p>
<p>
Within the review period, the Designated Expert(s) will either approve or
deny the registration request, communicating this decision to the review list and IANA.
Denials should include an explanation and, if applicable, suggestions as to how to make
the request successful.
</p>
<p>
IANA must only accept registry updates from the Designated Expert(s), and should direct
all requests for registration to the review mailing list.
</p>
<section id="registration-template">
<h4>Registration Template</h4>
<dl>
<dt>Error name:</dt>
<dd> <p>
The name requested (e.g., &quot;example&quot;).
Values for the error name MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
</p>
</dd>
<dt>Error usage location:</dt>
<dd> <p>
The location(s) where the error can be used. The possible locations are:
authorization code grant error response (<a href="#code-authz-error">Error Response</a>),
implicit grant error response (<a href="#implicit-authz-error">Error Response</a>),
token error response (<a href="#token-errors">Error Response</a>), or
resource access error response (<a href="#resource-errors">Error Response</a>).
</p>
</dd>
<dt>Related protocol extension:</dt>
<dd> <p>
The name of the extension grant type, access token type, or extension parameter,
the error code is used in conjunction with.
</p>
</dd>
<dt>Change controller:</dt>
<dd> <p>
For standards-track RFCs, state &quot;IETF&quot;. For others, give the name of the
responsible party. Other details (e.g., postal address, e-mail address, home page
URI) may also be included.
</p>
</dd>
<dt>Specification document(s):</dt>
<dd> <p>
Reference to the document that specifies the error code, preferably including a URI
that can be used to retrieve a copy of the document. An indication of the relevant
sections may also be included, but is not required.
</p>
</dd>
</dl>
</section>
</section>
</section>
<section class="references">
<h2>References</h2>
<ol>
<li id="usascii">
Coded Character Set -- 7-bit American Standard Code for Information Interchange
(ANSI X3.4),
1986
</li>
<li id="i-d-draft-hardt-oauth-01">
OAuth Web Resource Authorization Profiles
,
January 2010
</li>
</ol>
</section>
<section class="appendix">
<h2>Appendix</h2>
<section id="augmented-backus-naur-form-abnf-syntax" class="back">
<h3>Augmented Backus-Naur Form (ABNF) Syntax</h3>
<p>
This section provides Augmented Backus-Naur Form (ABNF) syntax
descriptions for the elements defined in this specification
using the notation of <a href="#rfc5234">RFC5234</a>.
The ABNF below is defined in terms of
Unicode code points <a href="#w3c-rec-xml-20081126">W3C.REC-xml-20081126</a>;
these characters are typically encoded in UTF-8.
Elements are presented in the order first defined.
</p>
<p>
Some of the definitions that follow use the
URI-reference
definition from <a href="#rfc3986">RFC3986</a>.
</p>
<figure>
<p class="preamble">
Some of the definitions that follow use these common definitions:
</p>
<pre>
VSCHAR = %x20-7E
NQCHAR = %x21 / %x23-5B / %x5D-7E
NQSCHAR = %x20-21 / %x23-5B / %x5D-7E
UNICODECHARNOCRLF = %x09 /%x20-7E / %x80-D7FF /
%xE000-FFFD / %x10000-10FFFF</pre>
</figure>
<p>
(The UNICODECHARNOCRLF definition is based upon the Char definition in
Section 2.2 of <a href="#w3c-rec-xml-20081126">W3C.REC-xml-20081126</a>, but omitting the
Carriage Return and Linefeed characters.)
</p>
<section id="client_id-syntax">
<h4>&quot;client_id&quot; Syntax</h4>
<figure>
<p class="preamble">
The client_id element is defined in
<a href="#client-password">Client Password</a>:
</p>
<pre>
client-id = *VSCHAR</pre>
</figure>
</section>
<section id="client_secret-syntax">
<h4>&quot;client_secret&quot; Syntax</h4>
<figure>
<p class="preamble">
The client_secret element is defined in
<a href="#client-password">Client Password</a>:
</p>
<pre>
client-secret = *VSCHAR</pre>
</figure>
</section>
<section id="response_type-syntax">
<h4>&quot;response_type&quot; Syntax</h4>
<figure>
<p class="preamble">
The response_type element is defined in
<a href="#response-type">Response Type</a> and
<a href="#response-type-ext">Defining New Authorization Endpoint Response Types</a>:
</p>
<pre>
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
</section>
<section id="scope-syntax">
<h4>&quot;scope&quot; Syntax</h4>
<figure>
<p class="preamble">
The scope element is defined in
<a href="#scope">Access Token Scope</a>:
</p>
<pre>
scope = scope-token *( SP scope-token )
scope-token = 1*NQCHAR</pre>
</figure>
</section>
<section id="state-syntax">
<h4>&quot;state&quot; Syntax</h4>
<figure>
<p class="preamble">
The state element is defined in
<a href="#code-authz-req">Authorization Request</a>,
<a href="#code-authz-resp">Authorization Response</a>,
<a href="#code-authz-error">Error Response</a>,
<a href="#implicit-authz-req">Authorization Request</a>,
<a href="#implicit-authz-resp">Access Token Response</a>, and
<a href="#implicit-authz-error">Error Response</a>:
</p>
<pre>
state = 1*VSCHAR</pre>
</figure>
</section>
<section id="redirect_uri-syntax">
<h4>&quot;redirect_uri&quot; Syntax</h4>
<figure>
<p class="preamble">
The redirect_uri element is defined in
<a href="#code-authz-req">Authorization Request</a>,
<a href="#token-req">Access Token Request</a>, and
<a href="#implicit-authz-req">Authorization Request</a>:
</p>
<pre>
redirect-uri = URI-reference</pre>
</figure>
</section>
<section id="error-syntax">
<h4>&quot;error&quot; Syntax</h4>
<figure>
<p class="preamble">
The error element is defined in
<a href="#code-authz-error">Error Response</a>,
<a href="#implicit-authz-error">Error Response</a>,
<a href="#token-errors">Error Response</a>,
<a href="#resource-errors">Error Response</a>, and
<a href="#new-errors">Defining Additional Error Codes</a>:
</p>
<pre>
error = 1*NQSCHAR</pre>
</figure>
</section>
<section id="error_description-syntax">
<h4>&quot;error_description&quot; Syntax</h4>
<figure>
<p class="preamble">
The error_description element is defined in
<a href="#code-authz-error">Error Response</a>,
<a href="#implicit-authz-error">Error Response</a>,
<a href="#token-errors">Error Response</a>, and
<a href="#resource-errors">Error Response</a>:
</p>
<pre>
error-description = 1*NQSCHAR</pre>
</figure>
</section>
<section id="error_uri-syntax">
<h4>&quot;error_uri&quot; Syntax</h4>
<figure>
<p class="preamble">
The error_uri element is defined in
<a href="#code-authz-error">Error Response</a>,
<a href="#implicit-authz-error">Error Response</a>,
<a href="#token-errors">Error Response</a>, and
<a href="#resource-errors">Error Response</a>:
</p>
<pre>
error-uri = URI-reference</pre>
</figure>
</section>
<section id="grant_type-syntax">
<h4>&quot;grant_type&quot; Syntax</h4>
<figure>
<p class="preamble">
The grant_type element is defined in
<a href="#token-req">Access Token Request</a>,
<a href="#password-tok-req">Access Token Request</a>,
<a href="#client-req">Access Token Request</a>,
<a href="#token-refresh">Refreshing an Access Token</a>, and
<a href="#ext-grant">Extension Grants</a>:
</p>
<pre>
grant-type = grant-name / URI-reference
grant-name = 1*name-char
name-char = &quot;-&quot; / &quot;.&quot; / &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
</section>
<section id="code-syntax">
<h4>&quot;code&quot; Syntax</h4>
<figure>
<p class="preamble">
The code element is defined in
<a href="#token-req">Access Token Request</a>:
</p>
<pre>
code = 1*VSCHAR</pre>
</figure>
</section>
<section id="access_token-syntax">
<h4>&quot;access_token&quot; Syntax</h4>
<figure>
<p class="preamble">
The access_token element is defined in
<a href="#implicit-authz-resp">Access Token Response</a> and
<a href="#token-response">Successful Response</a>:
</p>
<pre>
access-token = 1*VSCHAR</pre>
</figure>
</section>
<section id="token_type-syntax">
<h4>&quot;token_type&quot; Syntax</h4>
<figure>
<p class="preamble">
The token_type element is defined in
<a href="#implicit-authz-resp">Access Token Response</a>,
<a href="#token-response">Successful Response</a>, and
<a href="#new-types">Defining Access Token Types</a>:
</p>
<pre>
token-type = type-name / URI-reference
type-name = 1*name-char
name-char = &quot;-&quot; / &quot;.&quot; / &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
</section>
<section id="expires_in-syntax">
<h4>&quot;expires_in&quot; Syntax</h4>
<figure>
<p class="preamble">
The expires_in element is defined in
<a href="#implicit-authz-resp">Access Token Response</a> and
<a href="#token-response">Successful Response</a>:
</p>
<pre>
expires-in = 1*DIGIT</pre>
</figure>
</section>
<section id="username-syntax">
<h4>&quot;username&quot; Syntax</h4>
<figure>
<p class="preamble">
The username element is defined in
<a href="#password-tok-req">Access Token Request</a>:
</p>
<pre>
username = *UNICODECHARNOCRLF</pre>
</figure>
</section>
<section id="password-syntax">
<h4>&quot;password&quot; Syntax</h4>
<figure>
<p class="preamble">
The password element is defined in
<a href="#password-tok-req">Access Token Request</a>:
</p>
<pre>
password = *UNICODECHARNOCRLF</pre>
</figure>
</section>
<section id="refresh_token-syntax">
<h4>&quot;refresh_token&quot; Syntax</h4>
<figure>
<p class="preamble">
The refresh_token element is defined in
<a href="#token-response">Successful Response</a> and
<a href="#token-refresh">Refreshing an Access Token</a>:
</p>
<pre>
refresh-token = 1*VSCHAR</pre>
</figure>
</section>
<section id="endpoint-parameter-syntax">
<h4>Endpoint Parameter Syntax</h4>
<figure>
<p class="preamble">
The syntax for new endpoint parameters is defined in
<a href="#endpoint-params">Defining New Endpoint Parameters</a>:
</p>
<pre>
param-name = 1*name-char
name-char = &quot;-&quot; / &quot;.&quot; / &quot;_&quot; / DIGIT / ALPHA</pre>
</figure>
</section>
</section>
<section id="urlencoded" class="back">
<h3>Use of application/x-www-form-urlencoded Media Type</h3>
<p>
At the time of publication of this specification, the
application/x-www-form-urlencoded
media type was defined in Section 17.13.4 of
<a href="#w3c-rec-html401-19991224">W3C.REC-html401-19991224</a>, but not
registered in the IANA media types registry
(&lt;http://www.iana.org/assignments/media-types/index.html&gt;).
Furthermore, that definition is incomplete, as it does not
consider non-US-ASCII characters.
</p>
<p>
To address this shortcoming when generating payloads using
this media type, names and values MUST be encoded using the
UTF-8 character encoding scheme <a href="#rfc3629">RFC3629</a> first;
the resulting octet sequence then needs to be further encoded using
the escaping rules defined in <a href="#w3c-rec-html401-19991224">W3C.REC-html401-19991224</a>.
</p>
<p>
When parsing data from a payload using this media type, the
names and values resulting from reversing the name/value
encoding consequently need to be treated as octet sequences,
to be decoded using the UTF-8 character encoding scheme.
</p>
<p>
For example, the value consisting of the six Unicode code points
(1) U+0020 (SPACE), (2) U+0025 (PERCENT SIGN), (3) U+0026
(AMPERSAND), (4) U+002B (PLUS SIGN), (5) U+00A3 (POUND SIGN),
and (6) U+20AC (EURO SIGN) would be encoded into the octet
sequence below (using hexadecimal notation):
</p>
<figure>
<pre>
20 25 26 2B C2 A3 E2 82 AC</pre>
</figure>
<p>
and then represented in the payload as:
</p>
<figure>
<pre>
+%25%26%2B%C2%A3%E2%82%AC</pre>
</figure>
</section>
<section id="acknowledgements" class="back">
<h3>Acknowledgements</h3>
<p>
The initial OAuth 2.0 protocol specification was edited by David Recordon, based on two
previous publications: the OAuth 1.0 community specification <a href="#rfc5849">RFC5849</a>, and
OAuth WRAP (OAuth Web Resource Authorization Profiles)
<a href="#i-d-draft-hardt-oauth-01">OAuth Web Resource Authorization Profiles</a>.
Eran Hammer then edited the drafts through draft -26.
The Security Considerations section was drafted
by Torsten Lodderstedt, Mark McGloin, Phil Hunt, Anthony Nadalin, and John Bradley.
The section on use of the application/x-www-form-urlencoded media type
was drafted by Julian Reschke.
The ABNF section was drafted by Michael B. Jones.
</p>
<p>
The OAuth 1.0 community specification was edited by Eran Hammer and authored by
Mark Atwood, Dirk Balfanz, Darren Bounds, Richard M. Conlan, Blaine Cook, Leah Culver,
Breno de Medeiros, Brian Eaton, Kellan Elliott-McCrea, Larry Halff, Eran Hammer,
Ben Laurie, Chris Messina, John Panzer, Sam Quigley, David Recordon, Eran Sandler,
Jonathan Sergent, Todd Sieling, Brian Slesinsky, and Andy Smith.
</p>
<p>
The OAuth WRAP specification was edited by Dick Hardt and authored by Brian Eaton,
Yaron Y. Goland, Dick Hardt, and Allen Tom.
</p>
<p>
This specification is the work of the OAuth Working Group, which includes dozens of active
and dedicated participants. In particular, the following individuals contributed ideas,
feedback, and wording that shaped and formed the final specification:
</p>
<p>
Michael Adams, Amanda Anganes, Andrew Arnott, Dirk Balfanz, Aiden Bell, John Bradley, Brian Campbell,
Scott Cantor, Marcos Caceres, Blaine Cook, Roger Crew, Brian Eaton, Wesley Eddy, Leah Culver,
Bill de hOra, Andre DeMarre, Brian Eaton, Wolter Eldering, Brian Ellin, Igor Faynberg,
George Fletcher, Tim Freeman, Luca Frosini, Evan Gilbert, Yaron Y. Goland, Brent Goldman,
Kristoffer Gronowski, Eran Hammer, Justin Hart, Dick Hardt, Craig Heath, Phil Hunt, Michael B. Jones,
Terry Jones, John Kemp, Mark Kent, Raffi Krikorian, Chasen Le Hara, Rasmus Lerdorf,
Torsten Lodderstedt, Hui-Lan Lu, Casey Lucas, Paul Madsen, Alastair Mair, Eve Maler,
James Manger, Mark McGloin, Laurence Miao, William Mills, Chuck Mortimore, Anthony Nadalin,
Julian Reschke, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre,
Marius Scurtescu, Naitik Shah, Luke Shepard, Vlad Skvortsov, Justin Smith, Haibin Song,
Niv Steingarten, Christian Stuebner, Jeremy Suriel, Paul Tarjan, Christopher Thomas,
Henry S. Thompson, Allen Tom, Franklin Tse, Nick Walker, Shane Weeden, and Skylar Woodward.
</p>
<p>
This document was produced under the chairmanship of Blaine Cook, Peter Saint-Andre,
Hannes Tschofenig, Barry Leiba, and Derek Atkins. The area directors included Lisa Dusseault,
Peter Saint-Andre, and Stephen Farrell.
</p>
</section>
<section id="document-history" class="back">
<h3>Document History</h3>
<p>
[[ to be removed by the RFC editor before publication as an RFC ]]
</p>
<p>
-31
</p>
<ul class="symbols">
<li> <p>
Clarify that any client can send client_id
but that sending it is only required when using the code flow
if the client is not otherwise authenticated.
</p>
</li>
<li> <p>
Removed David Recordon's name from the author list, at his request.
</p>
</li>
</ul>
<p>
</p>
<dl>
<dt>
-30
</dt>
<dd>
<p>
Added text explaining why the server_error
and temporarily_unavailable error codes
are needed.
</p>
</dd>
<dt>
-29
</dt>
<dd>
<p>
Added &quot;MUST&quot; to &quot;A public client that was not issued a client password
MUST use the client_id request parameter to
identify itself when sending requests to the token endpoint&quot;
and added text explaining why this must be so.
</p>
<p>
Added that the authorization server MUST
&quot;ensure the authorization code was issued to the authenticated
confidential client or to the public client identified by the
client_id in the request&quot;.
</p>
<p>
Added Security Considerations section
&quot;Misuse of Access Token to Impersonate Resource Owner in Implicit Flow&quot;.
</p>
<p>
Added references in the &quot;Implicit&quot; and &quot;Implicit Grant&quot;
sections to particularly pertinent security
considerations.
</p>
<p>
Added appendix &quot;Use of application/x-www-form-urlencoded Media Type&quot;
and referenced it in places that this encoding is used.
</p>
<p>
Deleted &quot;;charset=UTF-8&quot; from examples formerly using
&quot;Content-Type: application/x-www-form-urlencoded;charset=UTF-8&quot;.
</p>
<p>
Added the phrase &quot;with a character encoding of UTF-8&quot; when
describing how to send requests using the HTTP request entity-body.
</p>
<p>
For symmetry when using HTTP Basic authentication, also apply
the application/x-www-form-urlencoded
encoding to the client password, just as was already done for
the client identifier.
</p>
<p>
Added &quot;The ABNF below is defined in terms of Unicode code
points <a href="#w3c-rec-xml-20081126">W3C.REC-xml-20081126</a>;
these characters are typically encoded in UTF-8&quot;.
</p>
<p>
Replaced UNICODENOCTRLCHAR in ABNF with
UNICODECHARNOCRLF = %x09 / %x20-7E / %x80-D7FF / %xE000-FFFD / %x10000-10FFFF.
</p>
<p>
Corrected incorrect uses of &quot;which&quot;.
</p>
<p>
Reduced multiple blank lines around artwork elements to single blank lines.
</p>
<p>
Removed Eran Hammer's name from the author list, at his request.
Dick Hardt is now listed as the editor.
</p>
</dd>
<dt>
-28
</dt>
<dd>
<p>
Updated the ABNF in the manner discussed by the working
group, allowing username and
password to be Unicode and
restricting client_id and
client_secret to ASCII.
</p>
<p>
Specified the use of the application/x-www-form-urlencoded content-type
encoding method to encode the client_id
when used as the password for HTTP Basic.
</p>
</dd>
<dt>
-27
</dt>
<dd>
<p>
Added character set restrictions for error, error_description, and error_uri parameters consistent with the OAuth Bearer spec.
</p>
<p>
Added &quot;resource access error response&quot; as an error usage location in the OAuth Extensions Error Registry.
</p>
<p>
Added an ABNF for all message elements.
</p>
<p>
Corrected editorial issues identified during review.
</p>
</dd>
</dl>
</section>
</section>
</article>
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