[chat] On-the-fly user authentication

[Peter Faulks <peter@xxxxxxxxxxxxxxx>]

After a bit of advice.

I'm designing an end-user application that will be getting data updates
from a central server.

I can authenticate and check update status with cgi using a db and
session ids - that's no problem.

What I need is a way to add a session generated user/password
automagically so I can have basic HTTP authenication JUST FOR THAT
SESSION so I can pass a URI for a file name to d/l. The user/password
should expire (ie be removed) after (say) 15mins. 

Any clues as to how I could achive this in a non-server specific manner?
London to a brick it would be Apache, but no guarantees about which
modules are going to be available.

Thanks