Session Management and Authentication with PHPLIB

Let's face it, web pages aren't designed for interaction with users. At one time or another, you've probably found yourself needing to know what user you are dealing with, and some information about that user. But how do you do it on the web? There are many ways, but most of them are either error prone, or serious security risks. Passing around form data from page to page can easily be sniffed, and even more easily forged. What is a webmaster to do?