Mediation policy to call a backend and enrich payload in the request flow in WSO2 APIM

chainingSeq.xml

<sequence xmlns="http://ws.apache.org/ns/synapse" name="chainingSeq">
    <!-- reading the author ID-->
    <property name="uri.var.id" expression="json-eval($.author}" />
    <!-- copying the original payload to a variable-->
    <enrich>
        <source type="body" clone="true"/>
        <target type="property" property="original_request"/>
    </enrich>
    <!-- Saving the URL postfix that is required when calling the backend -->
    <property name="rest_postfix" expression="$axis2:REST_URL_POSTFIX"/>
    <property name="REST_URL_POSTFIX" scope="axis2" action="remove"/>
    <!-- calling the backend service to get the name of the author from the ID-->
    <call blocking="true">
        <endpoint>
            <http method="GET" uri-template="http://localhost:3000/profile/{uri.var.id}"/>
        </endpoint>
    </call>
    <!-- Extract the name from the payload-->
    <property name="author" expression="json-eval($.name}" />
    <!-- Restore the original request payload to the message flow -->
    <enrich>
        <source clone="false" xpath="$ctx:original_request"/>
        <target type="body"/>
    </enrich>
    <!-- Enrich the author name into the original payload -->
    <enrich>
        <source clone="true" property="author" type="property"/>
        <target action="replace" xpath="json-eval($.author)"/>
    </enrich>
    <!-- Setting back the URL postfix to call the backend endpoint -->
    <property name="REST_URL_POSTFIX" scope="axis2" action="set" expression="$ctx:rest_postfix"/>
</sequence>