In this article, we covered the basics of PAM configuration. We learned that PAM configuration is really just a series of stack entries. Each time a service requests PAM's help, the PAM routines simply call all the stack entries related to that service, in order. The process of adding authentication procedures for new services to the system is therefore as easy as adding a few new stack entries in the PAM configuration files.
Each stack entry in a PAM configuration file contains a module type to determine the context in which the stack entry will be run and a control flag to determine its importance. A module is also supplied that contains the actual code to process the task at hand.
Though PAM configuration can seem complex at first, it is actually not too difficult to master, and the online PAM documentation located at http://www.kernel.org/pub/linux/libs/pam/ can help quite a bit.