Description:
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Hi,

I couldn't find any piece oh information on php.net (french) about $_SERVER['HTTP_ORIGIN'].

I need it for some tests before sending an "Access-Control-Allow-Origin" header for cross-domain ajax requests:
Requests can be sent from different hosts, I must identify the sending host, check if allowed against an array of allowed domains, and if ok, send this header with the return to the request.

In particularly need information about following points: 
- when is this superglobal set? when is it NOT set? Do specific values exist (null, empty string?)?
- is it always reliable or client/browser dependant? 
- besides, some information about its content would be appreciated, but maybe it's http more than php documentation: is the subdomain, the protocol and/or the port important for the client to be able to get the ajax return? For instance, a request sent from a https://www.example.com hosted page and a header allowing http://example.com are they compatible?

Hereunder a little extract of code, to show how I need to use it. It works in my tests, but I'm not sure it's not problematic with other browsers...

Test script:
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if(isset($_SERVER['HTTP_ORIGIN'])) {// in case of cross domain ajax call
    $http_origin = $_SERVER['HTTP_ORIGIN']; 
    if(in_array($http_origin, $ajaxAllowedDomains))
       { header("Access-Control-Allow-Origin: $http_origin"); }
}