It's tricky, it's by design messy, and I don't encourage people to use it if possible not to.
First of all, apache driver can't handle groups. That's, as far as I know, and what I can read from the source, on answers on internet, and from the not-existing documentation, it's actually impossible to get groups out of apache auth/n//z/-modules to PHP. There isn't any infrastructures for it at all. Groups only exist within each auth module in apache. That means, using apache modules, you loose all benefits of using groups, and set permissions on groups.