Mod_Authz_Unixgroup 1.0.x is a unix group access control modules for Apache
version 2.2.  If you have Apache 2.3 or Apache 2.4, you should be using
version 1.1.x of this module instead.

If you are having users authenticate with real Unix login ID over the net,
using something like my mod_authnz_external / pwauth combination, and you
want to do access control based on unix group membership, then
mod_authz_unixgroup is exactly what you need.

WWW: http://www.unixpapa.com/mod_authz_unixgroup/