Parse reverse proxy headers.

Assumes the following config in nginx:

                proxy_set_header  X-Real-IP $remote_addr;
                proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header  X-Forwarded-Proto $scheme;
                proxy_set_header  Host $http_host;
                proxy_pass_header Server;
                proxy_pass_header Host;