I'd love to tell you what I'm trying to do: But I'm not really sure yet.

Clearly, it's hard to ask for advice on an issue that's not fully fleshed out.

It's just that so many webapps today need to have user authentication/profile management, it seems a shame to have to build your own for two reasons: 1) You're wasting your time building something. 2) People trust you with their personal information, I think people are more willing to trust, say, a facebook, then they are joestartup.com. I say this based on my intuition.