[Koha] Koha is not authorized to use CAS

Hi everyone, I'm trying to implement KOHA library to my university. I' using KOHA 3.18 and Ubuntu server 14.04 TLS. I followed instructions on how to install KOHA from here http://wiki.koha-community.org/wiki/Koha_on_ubuntu_-_packages I needed to do SSO with CAS (4.0.0). So far, I managed to login to CAS as default CAS user. When I try to login as patron I get the error 'The application you attempted to authenticate is not authorized to use CAS'. I would like to know how to authenticate KOHA with CAS, how to login to CAS as Koha patron. I would appreciate any help Kind regards, Ahmed