Server-side hooks for user session start and session end

Hi all,

I'm trying to find a soultion to automatically execute something
(preferrably a function or at least some pure sql statements) at the
beginning and at the end of a user session. As an example, imagine just
storing of all login and logout timestamps (though the real task is a
bit more complicated than that)

I would not like it to be somehow explicitely client-side initiated
(like e.g. trivially calling some certain do_at_sess_begin(),
do_at_sess_end()) because first, a malicious client could then mess it
up easily, and furthermore, in the case that the session somehow ended
abnormally (due to say temporary network fault) client-side finalizer
function would not be called anyway.

My first try was to create an event trigger for sql drop events, then
create a temporary table and watch for its drop at the end of a session.
However, it seems drop events are just not fired for temporary tables
(although documentation does not state this anywhere, as far as I can
see, maybe I'm wrong about that)

It would seem like one of the simplest things ever, but I'm now totally
stuck out of ideas.

As a partial solution, handling just session _end_ would already be OK.

Any thoughts?

Thank you,
Nikolai