User login using session algorithm

I'm planning to write a simple user login module. I want it to be a stand-alone class, and not rely on cookies (I'm passing all variables via GET method anyways, so I just want to pass a session ID in the URL). Before I go ahead and do some mistake, could somebody have a look at the outline of the algorithm I've come up with? Any opinions greately appreciated. http://www.thpoon.com/~antipode/tmp/user_auth.png The algorithm is presented as a flowchart. p.s. I'd like to "roll my own", even though I know that there is authentication code available. Many thanks, -- Arcady Genkin Nostalgia isn't what it used to be.