How to make a GET request and place parameters in the header

I read on one of the Google pages for its 开发者_如何学JAVAOAuth mechanism that you can send a OAuthGetRequestToken request by using the:

Authorization header of a GET or POST request. Use "Authorization: OAuth". All parameters listed above can go in the header, except for scope and xoauth_displayname, which must go either in the body or in the URL as a query parameter.

I've been looking around the web for quite awhile now as to what this means. Can anybody clear this up for me? And I'm not sure if it's relevant, but I use PHP as my scripting language so any information specific to php would be appreciated. More specifically:

-How do you send a header with additional information?

-How do you read back the header?

Why not use the OAuth extension?