MadPenguin.org published a Linux Pluggable Authentication Module (PAM) Overview
Authentication is the process in which a program determines whether a user is actually the person who he claims to be. It is used in any kind of a system that provides different services to people depending upon their membership. When you log in to your favorite mailbox, access ATM, or use the services of Net Banking; what you are actually doing is obtaining service from the service provider after proving your credibility using your credentials (i.e. generally your user name and password).Linux Pluggable Authentication Module (PAM) Overview
