"external" variables and triggers

Hi there,

I have a problem that I'm not even 100% certain of how to word:

I'm writing a little postgres-app with a web-frontend. I was
going to map users to actual postgres users, but someone
on irc.freenode.net#postgresql was adamant that that was
bad practice and posed a security risk.

So I changed my plan and put user-IDs and md5 password-
hashes into a table of their own.

My problem now is that I'm using a separate table to keep
track of changes to the status of another one, trying to keep
the name, the date and a field called status. My problem is
that I can't figure out how to pass the user name (that has
been authenticated via a table and some php) to my trigger.

Can this be achieved at all?

If it can't, I'd rather re-create the database again and use
native postgres users (unless of course it REALLY is a
horrible security risk) than implement a whole lot of logic
in a language I'm not that familiar with.

Thanks for your patience reading this :)

Cheers,
Andrej