Do not attempt to use this provider if not shibboleth user has been set
This is needed for firewall to grant anonymous access to resources that accept it
Perform local logout if shib-logouturl has NOT been specified
* commented out check for authenticated shibboleth session in the request before proceeding handling the request by the shibboleth firewall listener
* fixed logout handler to also use the optional return url argument if no idp logout url is found in the request