User authentication tracing

[Davide Dozza]

Is it possible to trace Samba authenticated user?

That is, after a user has been authenticated versus a Samba acting
as PDC, is it possible to know if such user is still connected to the
Microsoft
network or they have been disconnected?
What I would like to do is to use Samba as authentication server in
order
to grant the access to other services (for example Internet navigation
through a proxy) and remove the access when such user disconnects
from the network.

Davide