wpCAS

wpCAS integrates WordPress into an established CAS architecture, allowing centralized management and authentication of user credentials in a heterogeneous environment.

From Wikipedia:

The Central Authentication Service (CAS) is a single sign-on protocol for the web. Its purpose is to permit a user to log into multiple applications simultaneously and automatically. It also allows untrusted web applications to authenticate users without gaining access to a user’s security credentials, such as a password. The name CAS also refers to a software package that implements this protocol.

Users who attempt to login to WordPress are redirected to the central CAS sign-on screen. After the user’s credentials are verified, s/he is then redirected back to the WordPress site. If the CAS username matches the WordPress username, the user is recognized as valid and allowed access.

Authorization of that user’s capabilities is based on native WordPress settings and functions. CAS only authenticates that the user is who s/he claims to be.

If the CAS user does not have an account in the WordPress site, an administrator defined function can be called to provision the account or do other actions. By default, CAS users without WordPress accounts are simply refused access.