Perl AuthCAS is a CAS 2.0 client Perl library.
The perl client AuthCAS is on CPAN: http://search.cpan.org/~osalaun/AuthCAS-1.1/lib/AuthCAS.pm
It should be packaged for Debian soon. More details at : http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=494849
There is also http://search.cpan.org/dist/Authen-CAS-Client/ which seems somewhat similar.

The repository seems gone, which is sad because I am using it to CASify otrs, and I bet there are loads of other CASifications that depend on this. Right now Im using http://web.archive.org/web/20060515184456/http://sourcesup.cru.fr/perlcas/ however the tarball seems to be damaged in the waybackmachine.