Linux PAM
Links
The primary distribution site for the Linux-PAM (Pluggable Authentication Modules for Linux) project
Linux-PAM @ GitHub
The Linux-PAM System Administrators' Guide
The Linux-PAM Module Writers' Guide
The Linux-PAM Application Developers' Guide
How to Configure and Use PAM in Linux
Configure and Use Linux-PAM
An introduction to Pluggable Authentication Modules (PAM) in Linux
PAM (german)
The Linux-PAM Guides
How is PAM checking the user password in unprivileged processes?
Understanding pam_unix and unix_chkpwd