This is pam_stack, a module for implementing recursive stacking with
Linux-PAM.  Because it's naughty and accesses some of the internals of
libpam, it's not likely that it can be made to work on anything but
Linux-PAM on Linux, FreeBSD, and other OSs that use Linux-PAM.

In a nutshell, calling pam_stack diverts a PAM stack into another
configuration file.  If the substack executes successfully, pam_stack
returns PAM_SUCCESS.  If the substack fails, pam_stack returns the
error code returned by the internal PAM dispatching routines, which
is typically the code returned by the module that failed.

This is primarily of use for when you want a consistent authentication
model for all of your system services, but want to allow the specifics
to change from service to service (like whether or not to use pam_rootok
or pam_securetty).

The module takes only two arguments:
debug		log lots of information to the system log
service=NAME	use as a substack the stack defined for the NAME service,
		usually the name of a file in /etc/pam.d

Nalin Dahyabhai <nalin@redhat.com>