Add the option for a return URL when generating the logout URL.

library/Unl/Cas.php

@@ -261,9 +261,13 @@ class Unl_Cas
      * Returns the URL to the CAS logout page.
      * Intended usage: $this->_redirect($cas->getLogoutUrl());
      */
-    public function getLogoutUrl()
+    public function getLogoutUrl($returnUrl = '')
     {
-        return $this->_casUrl . '/logout';
+        $url = $this->_casUrl . '/logout';
+        if ($returnUrl) {
+        	$url .= '?url=' . urlencode($returnUrl);
+        }
+        return $url;
     }
 
     /**