title: How to forward client ip to the backend in Google cloud ESP proxy
body: <p>I'm using Google Cloud ESP endpoint, and I want the ESP proxy to forward the clients IPs to the backend service for analytics purposes. From the Google docs I found that I should use <code>--add_request_header</code> to add headers to the request, and from the envoy docs (ESP is based on envoy proxy) they say the remote client IP is in the variable <code>x-envoy-external-address</code>, so I want to know how combine all things together and pass the clients IPs to the backend service in the args section upon ESP startup?</p>
  <p>Another thing, how to force HTTPS traffic only by the ESP? and will that redirect HTTP requests (clients) automatically to HTTPS?</p>