hope this isn't too late for you. You can use the authz library inside apache to authenticate to AD. it should be pre-built into apache on linux.
Then just add this block to your httpd.conf file - this is an example for giving authorization to you /usr/local/nagios/share folder.
Allow from all
AuthName "Windom1 account login"
the tricky bit is navigating through your domain to find out how the group is defined. so will be something like the example below, but it's different for everybody based on how you structure your AD.
here's an example of for allowing access to anyone from the IT group if it's structured under groups, central, us, in the domain called DOMAIN.LOCAL
I had to look at an open source domain browser to find out if each level of the tree was a CN or an OU - frustratingly, I couldn't find that information out by using the standard "active directory users and computers" that comes with microsoft. I don't remember what tool I used though - maybe one of these will work for you.
technet.microsoft.com/en-us/scri ... 39958.aspx
you can also use the dsquery command in a windows shell to query active directory