error resolving rss feed address using php script

I am endevouring to allow members only to access feed xml files. I have the redirect working in .htaccess. When I redirect to the checkAuth.php file I get the above error. The error is generated by CastFeed(HTTP/1.1 404 Not Found). I stripped out the auth part in order to get the access part right. My php file -

<?php
/**
* This script is used to authenticate a user based solely on a name passed as 
* the first parameter. The authentication is done against a mySQL db.
* 
*/
$file = "SFAPremium_f.xml";
header('Location: ' . "http://ift.tt/1wlFcle");
header('Content-type: content=text/xml');
header('Content-Disposition: filename="SFAPremium_f.xml"');
header('Content-length: ' . filesize($file));
readfile($file);
?>

Thanks.