authenticating Squeak to a proxy

Hello,

 I am new to Squeak (but not OO programming), and reading the "Squeak by
Example" book, but I can't figure out how to get Squeak to use a proxy that
requires authentication.  When at home, this is not a problem, but at my
school, I can only access the Internet through an HTTP proxy, and it
requires that each student enter his or her username and password.  I've
found where in Squeak I need to tell it what port to use, and the server
name, but there's nothing there for a username or passkey.  Is there a way
to tell Squeak to authenticate itself as a particular user?

Thanks,
Aidan