This is a port of mod_authz_unixgroup for apache22, written by Jan Wolter.

Mod_Authz_Unixgroup is a unix group access control modules for Apache 2.1 and
later.  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/