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cognito-authorizer
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console.log('Loading function'); | |
var jwt = require('jsonwebtoken'); | |
var request = require('request'); | |
var jwkToPem = require('jwk-to-pem'); | |
var userPoolId = 'us-east-2_xxxxxxxxxx'; | |
var region = 'us-east-2'; //e.g. us-east-1 | |
var iss = 'https://cognito-idp.' + region + '.amazonaws.com/' + userPoolId; | |
var pems; | |
exports.handler = function(event, context) { | |
//Download PEM for your UserPool if not already downloaded | |
if (!pems) { | |
//Download the JWKs and save it as PEM | |
request({ | |
url: iss + '/.well-known/jwks.json', | |
json: true | |
}, function (error, response, body) { | |
if (!error && response.statusCode === 200) { | |
pems = {}; | |
var keys = body['keys']; | |
for(var i = 0; i < keys.length; i++) { | |
//Convert each key to PEM | |
var key_id = keys[i].kid; | |
var modulus = keys[i].n; | |
var exponent = keys[i].e; | |
var key_type = keys[i].kty; | |
var jwk = { kty: key_type, n: modulus, e: exponent}; | |
var pem = jwkToPem(jwk); | |
pems[key_id] = pem; | |
} | |
//Now continue with validating the token | |
ValidateToken(pems, event, context); | |
} else { | |
//Unable to download JWKs, fail the call | |
context.fail("error"); | |
} | |
}); | |
} else { | |
//PEMs are already downloaded, continue with validating the token | |
ValidateToken(pems, event, context); | |
}; | |
}; | |
function ValidateToken(pems, event, context) { | |
var token = event.authorizationToken; | |
//Fail if the token is not jwt | |
var decodedJwt = jwt.decode(token, {complete: true}); | |
if (!decodedJwt) { | |
console.log("Not a valid JWT token"); | |
context.fail("Unauthorized"); | |
return; | |
} | |
//Fail if token is not from your UserPool | |
if (decodedJwt.payload.iss != iss) { | |
console.log("invalid issuer"); | |
context.fail("Unauthorized"); | |
return; | |
} | |
//Reject the jwt if it's not an 'Access Token' | |
if (decodedJwt.payload.token_use != 'access') { | |
console.log("Not an access token"); | |
context.fail("Unauthorized"); | |
return; | |
} | |
//Get the kid from the token and retrieve corresponding PEM | |
var kid = decodedJwt.header.kid; | |
var pem = pems[kid]; | |
if (!pem) { | |
console.log('Invalid access token'); | |
context.fail("Unauthorized"); | |
return; | |
} | |
//Verify the signature of the JWT token to ensure it's really coming from your User Pool | |
jwt.verify(token, pem, { issuer: iss }, function(err, payload) { | |
if(err) { | |
context.fail("Unauthorized"); | |
} else { | |
//Valid token. Generate the API Gateway policy for the user | |
//Always generate the policy on value of 'sub' claim and not for 'username' because username is reassignable | |
//sub is UUID for a user which is never reassigned to another user. | |
var principalId = payload.sub; | |
//Get AWS AccountId and API Options | |
var apiOptions = {}; | |
var tmp = event.methodArn.split(':'); | |
var apiGatewayArnTmp = tmp[5].split('/'); | |
var awsAccountId = tmp[4]; | |
apiOptions.region = tmp[3]; | |
apiOptions.restApiId = apiGatewayArnTmp[0]; | |
apiOptions.stage = apiGatewayArnTmp[1]; | |
var method = apiGatewayArnTmp[2]; | |
var resource = '/'; // root resource | |
if (apiGatewayArnTmp[3]) { | |
resource += apiGatewayArnTmp[3]; | |
} | |
//For more information on specifics of generating policy, refer to blueprint for API Gateway's Custom authorizer in Lambda console | |
var policy = new AuthPolicy(principalId, awsAccountId, apiOptions); | |
policy.allowAllMethods(); | |
context.succeed(policy.build()); | |
} | |
}); | |
} | |
/** | |
* AuthPolicy receives a set of allowed and denied methods and generates a valid | |
* AWS policy for the API Gateway authorizer. The constructor receives the calling | |
* user principal, the AWS account ID of the API owner, and an apiOptions object. | |
* The apiOptions can contain an API Gateway RestApi Id, a region for the RestApi, and a | |
* stage that calls should be allowed/denied for. For example | |
* { | |
* restApiId: "xxxxxxxxxx", | |
* region: "us-east-1", | |
* stage: "dev" | |
* } | |
* | |
* var testPolicy = new AuthPolicy("[principal user identifier]", "[AWS account id]", apiOptions); | |
* testPolicy.allowMethod(AuthPolicy.HttpVerb.GET, "/users/username"); | |
* testPolicy.denyMethod(AuthPolicy.HttpVerb.POST, "/pets"); | |
* context.succeed(testPolicy.build()); | |
* | |
* @class AuthPolicy | |
* @constructor | |
*/ | |
function AuthPolicy(principal, awsAccountId, apiOptions) { | |
/** | |
* The AWS account id the policy will be generated for. This is used to create | |
* the method ARNs. | |
* | |
* @property awsAccountId | |
* @type {String} | |
*/ | |
this.awsAccountId = awsAccountId; | |
/** | |
* The principal used for the policy, this should be a unique identifier for | |
* the end user. | |
* | |
* @property principalId | |
* @type {String} | |
*/ | |
this.principalId = principal; | |
/** | |
* The policy version used for the evaluation. This should always be "2012-10-17" | |
* | |
* @property version | |
* @type {String} | |
* @default "2012-10-17" | |
*/ | |
this.version = "2012-10-17"; | |
/** | |
* The regular expression used to validate resource paths for the policy | |
* | |
* @property pathRegex | |
* @type {RegExp} | |
* @default '^\/[/.a-zA-Z0-9-\*]+$' | |
*/ | |
this.pathRegex = new RegExp('^[/.a-zA-Z0-9-\*]+$'); | |
// these are the internal lists of allowed and denied methods. These are lists | |
// of objects and each object has 2 properties: A resource ARN and a nullable | |
// conditions statement. | |
// the build method processes these lists and generates the approriate | |
// statements for the final policy | |
this.allowMethods = []; | |
this.denyMethods = []; | |
if (!apiOptions || !apiOptions.restApiId) { | |
this.restApiId = "*"; | |
} else { | |
this.restApiId = apiOptions.restApiId; | |
} | |
if (!apiOptions || !apiOptions.region) { | |
this.region = "*"; | |
} else { | |
this.region = apiOptions.region; | |
} | |
if (!apiOptions || !apiOptions.stage) { | |
this.stage = "*"; | |
} else { | |
this.stage = apiOptions.stage; | |
} | |
}; | |
/** | |
* A set of existing HTTP verbs supported by API Gateway. This property is here | |
* only to avoid spelling mistakes in the policy. | |
* | |
* @property HttpVerb | |
* @type {Object} | |
*/ | |
AuthPolicy.HttpVerb = { | |
GET : "GET", | |
POST : "POST", | |
PUT : "PUT", | |
PATCH : "PATCH", | |
HEAD : "HEAD", | |
DELETE : "DELETE", | |
OPTIONS : "OPTIONS", | |
ALL : "*" | |
}; | |
AuthPolicy.prototype = (function() { | |
/** | |
* Adds a method to the internal lists of allowed or denied methods. Each object in | |
* the internal list contains a resource ARN and a condition statement. The condition | |
* statement can be null. | |
* | |
* @method addMethod | |
* @param {String} The effect for the policy. This can only be "Allow" or "Deny". | |
* @param {String} he HTTP verb for the method, this should ideally come from the | |
* AuthPolicy.HttpVerb object to avoid spelling mistakes | |
* @param {String} The resource path. For example "/pets" | |
* @param {Object} The conditions object in the format specified by the AWS docs. | |
* @return {void} | |
*/ | |
var addMethod = function(effect, verb, resource, conditions) { | |
if (verb != "*" && !AuthPolicy.HttpVerb.hasOwnProperty(verb)) { | |
throw new Error("Invalid HTTP verb " + verb + ". Allowed verbs in AuthPolicy.HttpVerb"); | |
} | |
if (!this.pathRegex.test(resource)) { | |
throw new Error("Invalid resource path: " + resource + ". Path should match " + this.pathRegex); | |
} | |
var cleanedResource = resource; | |
if (resource.substring(0, 1) == "/") { | |
cleanedResource = resource.substring(1, resource.length); | |
} | |
var resourceArn = "arn:aws:execute-api:" + | |
this.region + ":" + | |
this.awsAccountId + ":" + | |
this.restApiId + "/" + | |
this.stage + "/" + | |
verb + "/" + | |
cleanedResource; | |
if (effect.toLowerCase() == "allow") { | |
this.allowMethods.push({ | |
resourceArn: resourceArn, | |
conditions: conditions | |
}); | |
} else if (effect.toLowerCase() == "deny") { | |
this.denyMethods.push({ | |
resourceArn: resourceArn, | |
conditions: conditions | |
}) | |
} | |
}; | |
/** | |
* Returns an empty statement object prepopulated with the correct action and the | |
* desired effect. | |
* | |
* @method getEmptyStatement | |
* @param {String} The effect of the statement, this can be "Allow" or "Deny" | |
* @return {Object} An empty statement object with the Action, Effect, and Resource | |
* properties prepopulated. | |
*/ | |
var getEmptyStatement = function(effect) { | |
effect = effect.substring(0, 1).toUpperCase() + effect.substring(1, effect.length).toLowerCase(); | |
var statement = {}; | |
statement.Action = "execute-api:Invoke"; | |
statement.Effect = effect; | |
statement.Resource = []; | |
return statement; | |
}; | |
/** | |
* This function loops over an array of objects containing a resourceArn and | |
* conditions statement and generates the array of statements for the policy. | |
* | |
* @method getStatementsForEffect | |
* @param {String} The desired effect. This can be "Allow" or "Deny" | |
* @param {Array} An array of method objects containing the ARN of the resource | |
* and the conditions for the policy | |
* @return {Array} an array of formatted statements for the policy. | |
*/ | |
var getStatementsForEffect = function(effect, methods) { | |
var statements = []; | |
if (methods.length > 0) { | |
var statement = getEmptyStatement(effect); | |
for (var i = 0; i < methods.length; i++) { | |
var curMethod = methods[i]; | |
if (curMethod.conditions === null || curMethod.conditions.length === 0) { | |
statement.Resource.push(curMethod.resourceArn); | |
} else { | |
var conditionalStatement = getEmptyStatement(effect); | |
conditionalStatement.Resource.push(curMethod.resourceArn); | |
conditionalStatement.Condition = curMethod.conditions; | |
statements.push(conditionalStatement); | |
} | |
} | |
if (statement.Resource !== null && statement.Resource.length > 0) { | |
statements.push(statement); | |
} | |
} | |
return statements; | |
}; | |
return { | |
constructor: AuthPolicy, | |
/** | |
* Adds an allow "*" statement to the policy. | |
* | |
* @method allowAllMethods | |
*/ | |
allowAllMethods: function() { | |
addMethod.call(this, "allow", "*", "*", null); | |
}, | |
/** | |
* Adds a deny "*" statement to the policy. | |
* | |
* @method denyAllMethods | |
*/ | |
denyAllMethods: function() { | |
addMethod.call(this, "deny", "*", "*", null); | |
}, | |
/** | |
* Adds an API Gateway method (Http verb + Resource path) to the list of allowed | |
* methods for the policy | |
* | |
* @method allowMethod | |
* @param {String} The HTTP verb for the method, this should ideally come from the | |
* AuthPolicy.HttpVerb object to avoid spelling mistakes | |
* @param {string} The resource path. For example "/pets" | |
* @return {void} | |
*/ | |
allowMethod: function(verb, resource) { | |
addMethod.call(this, "allow", verb, resource, null); | |
}, | |
/** | |
* Adds an API Gateway method (Http verb + Resource path) to the list of denied | |
* methods for the policy | |
* | |
* @method denyMethod | |
* @param {String} The HTTP verb for the method, this should ideally come from the | |
* AuthPolicy.HttpVerb object to avoid spelling mistakes | |
* @param {string} The resource path. For example "/pets" | |
* @return {void} | |
*/ | |
denyMethod : function(verb, resource) { | |
addMethod.call(this, "deny", verb, resource, null); | |
}, | |
/** | |
* Adds an API Gateway method (Http verb + Resource path) to the list of allowed | |
* methods and includes a condition for the policy statement. More on AWS policy | |
* conditions here: http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html#Condition | |
* | |
* @method allowMethodWithConditions | |
* @param {String} The HTTP verb for the method, this should ideally come from the | |
* AuthPolicy.HttpVerb object to avoid spelling mistakes | |
* @param {string} The resource path. For example "/pets" | |
* @param {Object} The conditions object in the format specified by the AWS docs | |
* @return {void} | |
*/ | |
allowMethodWithConditions: function(verb, resource, conditions) { | |
addMethod.call(this, "allow", verb, resource, conditions); | |
}, | |
/** | |
* Adds an API Gateway method (Http verb + Resource path) to the list of denied | |
* methods and includes a condition for the policy statement. More on AWS policy | |
* conditions here: http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html#Condition | |
* | |
* @method denyMethodWithConditions | |
* @param {String} The HTTP verb for the method, this should ideally come from the | |
* AuthPolicy.HttpVerb object to avoid spelling mistakes | |
* @param {string} The resource path. For example "/pets" | |
* @param {Object} The conditions object in the format specified by the AWS docs | |
* @return {void} | |
*/ | |
denyMethodWithConditions : function(verb, resource, conditions) { | |
addMethod.call(this, "deny", verb, resource, conditions); | |
}, | |
/** | |
* Generates the policy document based on the internal lists of allowed and denied | |
* conditions. This will generate a policy with two main statements for the effect: | |
* one statement for Allow and one statement for Deny. | |
* Methods that includes conditions will have their own statement in the policy. | |
* | |
* @method build | |
* @return {Object} The policy object that can be serialized to JSON. | |
*/ | |
build: function() { | |
if ((!this.allowMethods || this.allowMethods.length === 0) && | |
(!this.denyMethods || this.denyMethods.length === 0)) { | |
throw new Error("No statements defined for the policy"); | |
} | |
var policy = {}; | |
policy.principalId = this.principalId; | |
var doc = {}; | |
doc.Version = this.version; | |
doc.Statement = []; | |
doc.Statement = doc.Statement.concat(getStatementsForEffect.call(this, "Allow", this.allowMethods)); | |
doc.Statement = doc.Statement.concat(getStatementsForEffect.call(this, "Deny", this.denyMethods)); | |
policy.policyDocument = doc; | |
return policy; | |
} | |
}; | |
})(); |
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