My understanding of how it works, this kind of thing is not possible. However, with a little creativity, you can work around it.
One solution would be to have users log in via group names, and not user names. Then, the root web page will have all the links available. And under each link dir, an .htaccess file will exist that will list all the groups who have valid access. If they have already logged in once, then that htaccess should recognize this and not bother asking for a password again. This would, though, require all link dirs available.
Your absolute best bet is a script, though. The script examines the HTTP header and looks for the username, then determines which group they're in and then displays all applicable links.
That is what I would suggest.