Add support for Apache authentication scheme

A customer has requested that we add support for the Apache Authentication Scheme.

Bugzilla can currently do this too as noted in their 2.20.1 release notes:

http://www.bugzilla.org/releases/2.20.1/release-notes.html:

"Environment Variable" Authentication Method -------------------------------------------- You can now tell Bugzilla to accept a certain value passed in from Apache as authentication for Bugzilla users. This means that Bugzilla now "supports" any type of authentication that Apache supports.