[gdm-list] Adding a user to a group on login

[Yan Seiner <yan seiner com>]

I'm trying to work something out....  It's not really a gdm question, 
but....

I've got specific resources tied to specific X screens.  So for example 
Display :3 gets /dev/scd1.

I'd like to set it up so that all the resources are available to a 
group, and the user loging in to that display is made a member of the 
group and then removed on logout.

So for example:

yan selene:~$ ls -l /dev/scd?
brw-rw---- 1 root   display2 11, 0 15. pro 09.03 /dev/scd0
brw-rw---- 1 root   display3 11, 1 15. pro 09.03 /dev/scd1


So if I were to log into a session with Display :3, I would be make a 
member of group display3, and could access that resource.  On logout, I 
would be removed.  Also, if gdm is killed, I would be removed.  I really 
want something temporary; I don't want to muck about with /etc/group if 
at all possible.

Any ideas?

--Yan