Plugin doesn't handle the "execution" parameter of CAS4

[chrismyers81]

After we upgraded to CAS 4.0.1, the plugin stopped successfully authenticating to our CAS server. I determined that the reason is because CAS4 has added a new hidden form parameter called "execution", and seems to typically use the default value of "e1s1" when no service parameter has been specified.

To resolve this, I manually modified the make_form section of the check_cas code and added the parameter statically, although it should probably pull the value of the form dynamically.

          make_form(
            entity   => $entity,
            username => $h_Option{'login'}{'value'},
            password => $h_Option{'authentication'}{'value'},
            lt       => $loginTicket,
            execution => 'e1s1',
            _eventId => 'submit'
          )