Since SMTP AUTH is an extension to the SMTP protocol itself, and qpsmtpd specifically claims to implement only the SMTP protocol, it makes more sense (to me anyways) to add a Qpsmtpd::Auth library module, instead of as a plugin. From my standpoint, that will be much easier to deal with, since I will want to have the authentication go against my vpopmail database instead of some textfile on the disk.
What I propose doing is taking what Ask Bjørn Hansen and Guillaume Filion have provided and turn it into an OO library. Then I will subclass that with a custom module which will use my chosen backend to authenticate against.
Wish me luck!
John
