Update: The CAS module is now maintained at drupal.org.

phpCAS is a fantastic library for integrating Central Authentication Services into PHP applications. The library is well-documented and is licensed under the LGPL. CAS is a Java-based single sign-on solution originally developed at Yale and later placed under the auspices of JA-SIG (Java Architectures - Special Interest Group). CAS has quickly become the most popular single sign-on solution for universities. In its most simple use (CAS can also proxy single sign-on), CAS authenticates users and sends the user to the requested application with a ticket. The application is then responsible for authenticating the ticket (behind the scenes, with a tool like cURL) and automatically logging the user in if the ticket is valid.

Using the excellent phpCAS library, we have created a small Drupal module to allow single sign-on with CAS. The latest release (0.4.20) of the phpCAS library is included in the download.