title: What is the HTTP header :host, :method, :path, :scheme, :version used for?
body: <p>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?</p>
  
  <p><img src="https://i.stack.imgur.com/iv9N3.png" alt="enter image description here"></p>
  
  <p>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.</p>