Get the origin of files via requested <link>

[eluser]seantaylor[/eluser]
I have a service that generates text files based on the url. So http://mysite.com/service/load/file1 would generate something useful, the point being text files can be generated dynamically based on url segements.

I can tell where the request is coming from when a user clicks a link using the $_SERVER['HTTP_REFERER'] method however this is not how I need the service to work. Instead I need a user to embed a <link> tag in their html to call the service in the style of
<link rel="stylesheet" href="http://mysite.com/service/load/file1" type="text/css"/>

Is there any way to tell when a file is requested through <link> where the request is coming from? I need this information to verify that the domain is privileged to access that file.