This is a replacement for the cas_sso plugin. It provides a middle man between a CAS server and a Discourse instance. It can actually supports any number of Discourse instances as long as they all use the same SSO api key. It also supports filtering the login via the CAS groups attributes if available.
The app is a very simple rails app and does not use a database at this point. If I ever get CAS SLO (Single LogOut) working that will require a database.