[squid-users] how to access username in an url_rewrite_program

Hi there,

we are running an application server behind squid (zope/plone).
Squid calls an url_rewrite_program written in python to call that server.
I would like to send the name of the authenticated user to the
application server.

Now my question: How can I do that?
For me the best thing would be to be able to add it to the http headers,
so that the server down the chain can read it.

how could I do that?
Is ther a sample somewher?

thanks a lot
robert