Percona created an auth plugin for MySQL that permits you to
authenticate users via PAM. Unfortunately it requires the libraries to
exist on both the client and server, so it's not suitable for bundling
with the client or the server. It's also compatible with other MySQL
implementations; I use it at work with vanilla MySQL 5.6.
The changes to percona56-server are required to permit this to be a
slave port and not inherit settings that are not applicable to this
port. It does not affect the client or server packages.