Cybercafe login-logout

[Nagy Attila István <tylla borsodi 7seas hu>]

Hi!

We are planning on developing a cybercafe software with client-server
architecture. The client should do the following:
 - the user can login with username/password
 - after the prepaid time expires the screen gets locked, and if the user
recharges his account it can log back in, otherways after a given period
other user can log in (the previous user gets logged off)
 - after a period of inactivity the screen gets locked, and the user can
log back in
 - there are other glitches like displaying the remaining time, and so on,
but those are less problematic.

As I googled a bit but did not found any related projects, I thought about
using the gdm for the main login-logout-lock things.
If you could help with any information about how somebody who is insider
in the gdm's design and structure would start fitting all these functions
into gdm I would really appreciate.
I started to analyze the source, but anyway is about 2 megs, so it would
be some time until I figure out the structure.

Thanks in advance for any help,
Tylla