Here is the documentation for Linux-PAM. As you will see it is currently not complete. However, in order of decreasing length:

• The System Administrators' Guide
• The Module Writers' Manual
• The Application developers' Manual

REVISION: $Id: index.html,v 1.4 1996/11/21 06:51:01 morgan Exp $ REVISION: $FreeBSD: src/contrib/libpam/doc/html/index.html,v 1.1.1.1.6.2 2001/06/11 15:28:10 markm Exp $ REVISION: $DragonFly: src/contrib/libpam/doc/html/Attic/index.html,v 1.2 2003/06/17 04:24:02 dillon Exp $