Password authentication through /etc/passwd

["Scott E Graves" <scott_e_graves@email.mobil.com>]

I'm in the process of writting a client/server application (purely in C) as a
pseudo-frontend to administer various aspects of Debian 2.2 from remote
locations over TCP/IP. What libraries do I need to look at in order to allow
client authentication against /etc/passwd? Authentication is currently being
performed through a simple text file housing a similar structure to /etc/passwd,
but I would like to bypass this and piggy-back off of /etc/passwd to allow
"true" UNIX authentication.

This is my first project developing under Linux, so any help would be greatly
appreciated.

Thanks,
Scott