Question about authentication

I'd like to be able to use XWiki with an alternate source for user authentication and I thought creating my own auth service might do the trick. However, on further thought, I'm not sure how this would work - doesn't the XWiki user document still need to exist as a place to store user settings (e.g email notification plugin stores an object there)? I dug around a bit in the LDAP service code, and don't see anywhere where it creates the xwiki user document, so I'm wondering what I'm missing. I was thinking that maybe it should should auth the user then create the user doc if it doesn't already exist. I guess the code/pages I have that register that user could also send a message to xwiki to create the user, but for LDAP user management clients that may not be possible, so I must be missing something. Is there a better way to do auth that I don't know about? Our user data is in a set of DB tables. Thanks, Matt