Any good lightweight User management libraries out there?

I’d like to put together an easy back end to an existing site (static) that allows registration, user management with permission levels and file uploads / downloads based on permissions.

Lightweight would be ideal, I don’t need much and there isn’t any chance of it being upgraded (as in functionality added). I thought about CodeIgnitor, Zend or other frameworks, but a framework seems overkill for such a simple project. I guess the fanciest I’d need is the ability to manage users and files (edit permissions, activate/de-activate users, remove or assign files to be viewable to a group).

I have no problems writing this myself, or even doing the bulk of it. However, I’d rather not re-invent the wheel if I don’t have to. Even pointing me to some well written, secure libraries would be much appreciated! (OOP if possible, secure, using prepared statements / PDO or something along those lines would be perfect).

I greatly appreciate any tips, advice or even criticism. Thanks!

Yii Framework would be a good option, easier in my opinion to start and understand. A framework should not be overkill for this project… otherwise you are re-inventing the wheel…

You can also have a look at phpclasses.org for related classes/implementations and combine them to work together.