检测访客来源（Facebook，雅虎，谷歌）等

Question

Im using single sign on solutions from jahrain. basically, i want to detect users coming from (facebook, yahoo, google, myspace, live/hotmail, openid) domains. then if not logged in. redirect to a webpage intended for these visitors. im using php.

Answer 1

While this is not foolproof, a common way to do this is by examining the $_SERVER['HTTP_REFERER'] environment variable, which is generally sent by the browser as a header.

That said, note the things from this thread: Determining Referer in PHP