on connect trigger?

Is there any kind of mechanism in pg 7.3 for doing something like what I
would describe as a "login trigger" procedure or maybe "on connect"
trigger, i.e., a way to specify a stored procedure to run when a user
connects to the database?

What I'm thinking is this. Right now, my end-user GUI application calls a
procedure which updates the user account expiration date whenever they
log in. The idea is that accounts that are never used will expire,
eventually, and those that are active will continually have the
expiration date pushed
further ahead each time they log in.

I'd like to not depend on the application making this call, because other
applications which connect to the same database will be written, and the
developers might not build in this same explicit procedure call -- it
really is the kind of thing that is best done on the backend.

~Berend Tober