In HTTP/1, a proxy client makes a CONNECT request with the name of the target server, the proxy server returns a 200 response (if it accepts it), and then the entire TCP connection becomes a tunnel to the target server. , and headers from the URL and header Optional, but recommended: Split Cookie headers into a separate header per cookie headers into a separate header per cookie Strip all headers made illegal in HTTP/2 messages: connection (and all headers listed in the value of the connection header) upgrade host http2-settings keep-alive proxy-connection transfer-encoding te (unless the value is just trailers )