The Citrix secure gateway is a piece of "freeware" software that comes with the installation cd-set. And is of course also downloadable from the mycitrix site. Thomas Koetzing and Victor Viudez configured a while ago add-on source code to the web interface 4.0 so you could say who can and who can't access the secure gateway with active directory groups.

I didn't notice that they have updated the software and it now supports the following web interfaces 4.0, 4.1, 4.2, 4,5 and 5.0.

You need to have the web interface default installed or otherwise modify the configuration yourself. I didn't test it yet but will soon testdrive this on my own secure gateway. Get the software here