The idea behind CAS is similar to the way Yahoo, Google, and other major portal sites allow the user to authenticate using a central welcome page, granting access all of their various services. The CAS server is the piece that provides the login page where the user enters their username and password. It then dishes out 'service tickets' to the various services that the user might try to access. With RubyCAS-Server, you can easily configure how the login page looks and how the username and password is validated (against a SQL database, Active Directory, LDAP, etc.)

CAS clients are available for most major web frameworks, including Java, PHP, Ruby on Rails. For more information on the CAS protocol, have a look at the official JA-SIG CAS page.

RubyCAS-Server is implemented using the Camping microframework, and is designed to be easily deployed as a stand-alone server or as a virtual host under Apache or other web servers. It fully implements the CAS 2.0 protocol, with full support for proxy ticketing.