Pluggable Authentication Modules: Threat or Menace?
PAM is one of the most misunderstood parts of systems administration. Many sysadmins live with authentication problems rather than risk making them worse. PAM's very nature makes it unlike any other Unix access control system.
If you have PAM misery or PAM mysteries, you need PAM Mastery
With PAM Mastery, you'll understand:

• the different versions of PAM
• the intricacies of Linux-PAM and OpenPAM
• how PAM policies make decisions
• how to debug PAM
• the most frequently seen PAM modules
• Linux-PAM extended controls and substacks
• time-based one-time passwords
• using SSH keys for more than SSH
• password quality testing
• policies from CentOS, Debian, and FreeBSD
• and more

Transform PAM from a headache to an ally with PAM Mastery