CAS and xymon

I am running xymon on a Ubuntu server and apache2.  I would like to place it behind CAS so I can better handle the access to the server.  I have the mod_auth_cas package installed and I have configured the conf file in /etc/apache2/mods-enabled/auth_cas.conf

I tried pointing the www directory to /var/www and /opt/xymon/server/www

Either way I do not get prompted for authentication.  I am not sure what I am missing.

Scott A. Dyer