Central Authentication Service, a trusted system to authenticate a user
A standards based, open source software package for web single sign-on across or within organizational boundaries.
The first shibboleth makes more sense to compare central authentication service cas with security assertion markup language saml which is the protocol used by shibboleth
Difference between Shibboleth and CAS?
Conceptually it seems like a type of central authentication system cas but is more similar to shibboleth also a federated identity management system
Where does ADFS fall in the classifications of authentication systems?