The Jasig Central Authentication Service was originally developed by Yale University. It has since become a Jasig project.
Since the availability of the Central Authentication Service server implementation and protocol, there have been many client programs developed for "CASifying" applications such that they can use CAS for user authentication.
What is Single sign-on?
Single sign on is a session/user authentication process that allows a user to provide his or her credentials once in order to access multiple applications. The single sign on authenticates the user to access all the applications he or she has been authorized to access. It eliminates future authenticaton requests when the user switches applications during that particular session.
Web Single sign on works strictly with applications accessed with a web browser. The request to access a web resource is intercepted either by a component in the web server, or by the application itself. Unauthenticated users are diverted to an authenticaton service and returned only after a successful authentication.