When visiting the site I get a CAS warning the variable is undeclared on line 25 of cas.php.

The hack by Vangelis Haniotakis to handle the absence of $_SERVER['REQUEST_URI'] in IIS doesn't work, you cannot check !$_SERVER['REQUEST_URI'], isset($_SERVER['REQUEST_URI']) should be used instead. The current one (using !) assumes the variable exists, returning a notice.

I've attached my copy that works, no errors or notices.