title: How to duplicate and forward a request with koa router
body: <p>For several reasons, I have a server that has to forward requests to another server. The response should be the response of the final server. I also need to add an extra header onto the request but remove this header again from the response before returning. As such, redirect isn't going to cut it.</p>
  <p>I'm currently doing it manually copying the headers &amp; body as required but I would like to know if there's a simple generic way to do it?</p>