Mod_authnz_ds is a project mainly written in ..., it's free.
A Directory Services authentication module for Apache.
This module provides authentication and authorization for Apache through Apple's Directory Services API.
From a command-line run: ./configure && sudo make install
Next, edit your httpd.conf file to add the following lines:
AuthName "<My Secured Site>"
AuthType DirectoryServices
Order allow,deny
Allow from all
Require group <special-people>