If you already have a shared user table, you only need session sharing. A piece that IMHO should be rewritten in CentralAuth, so perhaps it should be available as a separated piece. You can see some discussions about it in wikitech recently.
that would be brilliant. We have some resources and could contribute to testing and debugging, but we feel not ready to factor the single-sign-on code out of CentralAuth ourselves alone.
Who is interested in this? Maybe in a collaboration it becomes more likely.
Gregor