A login script is essentially so simple that it's not even worth dedicating a tutorial for that. Stuff involved is essentially form processing, database access and sessions/cookies. We have a tutorial for sessions and cookies and we have one for database access and another one focusing on joins and unions. Then you have form processing, but that's fairly straightforward. You simply read from the $_GET or $_POST superglobal. You might also be interested in this blog post that talks about breaking a script/application down into logical elements the same way I just did.