[mod_python] running script with the permissions of the authenticated system user

Hi

A client of mine wants me to write a simple web interface for qmail's
autorespond. this means that a user must authenticate with his system
user/password, and then make some changes to the files on the user home
directory. since this is done through NIS, it can't be done as root, and
must be done as the user.
I have 2 problems to solve:
1. authentication: the user must authenticate as a NIS user. this can
be done by apache, but the module to do that is still alpha. I prefer to
make it inside the script.
2. the script must run as the user authenticated. I can make it run as
root and run system commands with 'su' but I was wondering is there a
module in python to handle it.

any ideas?

thanx
-- 
Haim