Advice on central authentication system

We have a handful of applications in development and would like
people to use the same login/password for all of them. Since the
authentication module is shared it also needs to offer a remote API
for CRUD of users (basically).

The way we implement the remote calls is an important decision. I am
not yet familiar with Active Resource/Simply Restful, but this looks
like a paradigmatic scenario for them, right?

– fxn