How to set HTTP headers in a connector for WSO2 ESB

HTTP header fields are components of the message header of requests and responses in the Hypertext Transfer Protocol (HTTP). They define the operating parameters of an HTTP transaction. Most of the API calls requires to set some headers before making each API calls no matter its GET, POST or any other request type. 

In this post, I am going to focus on the headers that needs to be set for HTTP calls for Google Calendar REST API. 

API:                                   Google Calendar
Reference Link:                    https://developers.google.com/google-apps/calendar/v3/reference/

Headers need to be set :  Authorization , Content-Type

What do those headers mean?

Authorization : Authentication credentials for HTTP authentication

Content-Type: The MIME type of the body of the request

Now, let's see how to set those headers within the synapse template of the connector.It's quiet simple and the below code explain them to you.

<template name="test" xmlns="http://ws.apache.org/ns/synapse">

<!-- Set a parameter to get the access token  -->

<parameter name="accessToken"

description="The access token  of the Google Calendar API" />

<sequence>

<!-- Get the access token from the user  through synapse-->

<property name="uri.var.accessToken" expression="$func:accessToken" />

  <!--Set the access token as the Authorization transport header as below --> 

<property name="Authorization"

expression="fn:concat('Bearer ', get-property('uri.var.accessToken'))"

scope="transport" type="STRING" />

 <!-- Setting the Content-Type transport header as below-->

<property name="Content-Type" value="application/json" scope="transport"

type="STRING" />

<call>

<endpoint>

<!-- you can call the required end point from here  -->

</endpoint>

</call>

</sequence>

</template>

As you see above while setting the Authorization header i have used a concatenation function. That's because the authorization header should be set along with the ''Bearer" field concatenated with the access token. 

That's all about it. You can set any HTTP header by following the similar approach. Hope it was useful to you...