What is the HTTP header :host, :method, :path, :scheme, :version used for?

Question

I have seen that Twitter and Facebook is using :host, :method, :path, :scheme, :version in their HTTP requests. I just wonder what they are used for?

My first guess is that they use custom headers to prevent CSRF attacks. But you only need one header to prevent CSRF attacks not 5.

Answer 1

This might be SPDY or experimental HTTP/2.0. See http://greenbytes.de/tech/webdav/draft-ietf-httpbis-http2-09.html#HttpRequest