Best authentication system

Hi, I'm running a site for which I need an authentication system. I have already my own (that is too simplistic and not very secure). I want some advice here. I checked PEAR, but as there are several options there, I was not sure which one to choose. Here are my needs: - Some sections of the site cannot be accessed if the user does not have an account (at least login and password) - There are 2 type of users at this moment, depending on that type, the user can access some sections and not the others (the ones allowed for the other type). Maybe in the future there will be more types of users. Thank you