If you build Web applications, there are a few things you can’t dodge coding: a user registration workflow, a password reset workflow, a login and logout system, and so on. Since these workflows aren’t likely to change much from one project to another, why not package them all up in a set of classes and use the time you save on something more constructive (blowing up some Protoss bases, maybe?)
That’s the idea behind Sentry 2, which gives you a head start on your next PHP project by providing a framework for authentication and access control. For code and details, take a look at the first part of my IBM developerWorks article on Sentry 2 (part 2 will be published in a few weeks).