WSO2 API Manager & OAuth2 Protected Endpoint (Simple Mediation Sequence)

oauth2-sequence.xml

<?xml version="1.0" encoding="UTF-8"?>
<sequence name="oauth2-sequence" xmlns="http://ws.apache.org/ns/synapse">
    <!-- token generation to the oauth server's token endpoint -->
    <!-- add the base64 encoded credentials -->
    <property name="client-authorization-header" scope="default" type="STRING" value="MDZsZ3BTMnh0enRhOXBsaXZGUzliMnk4aEZFYTpmdE4yWTdLcnE2SWRsenBmZ1RuTVU1bkxjUFFh" />
    <property name="request-body" expression="json-eval($)" scope="default" type="STRING" />
    <property name="resource" expression="get-property('axis2', 'REST_URL_POSTFIX')" scope="default" type="STRING" />

    <!-- creating a request payload for client_credentials -->
    <payloadFactory media-type="xml">
        <format>
            <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
                <soapenv:Body>
                    <root xmlns="">
                        <grant_type>client_credentials</grant_type>
                    </root>
                </soapenv:Body>
            </soapenv:Envelope>
        </format>
        <args></args>
    </payloadFactory>

    <!-- set related headers to call the token endpoint -->
    <header name="Authorization" expression="fn:concat('Basic ', get-property('client-authorization-header'))" scope="transport" />
    <header name="Content-Type" value="application/x-www-form-urlencoded" scope="transport" />
    <property name="messageType" value="application/x-www-form-urlencoded" scope="axis2" type="STRING" />
    <property name="REST_URL_POSTFIX" value="" scope="axis2" type="STRING" />

    <!-- change the token endpoint -->
    <call blocking="true">
        <endpoint>
            <http method="POST" uri-template="https://localhost:9443/oauth2/token" />
        </endpoint>
    </call>

    <!-- append the acquired access token and make the call to the backend service -->
    <property name="bearer-token" expression="json-eval($.access_token)" scope="default" type="STRING" />
    <property name="REST_URL_POSTFIX" expression="get-property('resource')" scope="axis2" type="STRING" />
    <header name="Authorization" expression="fn:concat('Bearer ', get-property('bearer-token'))" scope="transport" />
    <payloadFactory media-type="json">
        <format>$1</format>
        <args>
            <arg evaluator="xml" expression="get-property('request-body')" />
        </args>
    </payloadFactory>
</sequence>