Review 19919

C. Thomas Tyler
Reviving LDAP group mirroring scripts, refactored into a different

These were deleted because the built-in LDAP authentication mechanism
provides a fully supported solution with similar functionality, and
since using built-in features is preferred for customers with no
compelling reason to use a custom solution.

However, some customers require Two Factor Authentication, and that
can only be achieved with old-school external authentication triggers
and supplemental custom automation.

This change introduces a new /p4/common/custom folder, with an 'auth'
subfolder as the first example of a custom module.  This folder is
intended to be for things that are to be distributed with SDP, but are
for customers with specific requirements that are not expected to be
broadly applicable.

The SDP solution would be an interim to provide a two-factor authentication
option until such time as that can be offered in the server.  As of July 2016,
adding built-in support for two-factor authentication is not on the Helix
Versioning Engine product roadmap (job048959).
Tip: Use n and p to cycle through the changes.