Custom User Account for Google App Engine - Part I

Google App Engine (GAE) is good. I like it, but...

Well, I create an app (in java), I want user to sign in, and GAE want the user to have google account. What if I don't want that, well, I can then implement my own user authentication, which is shit (cannot use request.getUserPrincipal()).
How about using OAuth... may be this can works.

I want to create 100 users to use my app but I don't want to create 100 google account.

Still a basic concept at the moment. Not sure if it will work. Will do an experiment soon.