Convert request parameter to an HTTP header in WSO2 ESB

Say, you have a requirement to pass a request parameter (named key) which comes to an ESB proxy service, and that need to be passed to the backend service as an HTTP header (named APIKEY).

Request to ESB proxy service would be as follows.

      curl -X GET "http://localhost:8280/services/MyPTProxy?key=67876gGXjjsskIISL

In that case you can make use of xpath expression $url:[param_name]

In your in-sequence you can add a header mediator as follows to set the HTTP header with key request parameter