Postfix-Smarthost authentication help?

[WA9ALS - John]

I'm running FC1, Postfix, and using a NAT router.  I just moved the machine
to a different ISP.  In contrast to the old ISP, the new ISP requires SMTP
authentication with username and password.

1.  Is there a place in Postfix where I can enter the authentication info?
There *IS* a place to enter the smarthost, but I don't see where I can enter
the auth info.

2.  Interestingly, when you run config.pl to setup SquirrelMail, there is a
place to enter authentication *mode*, e.g. "none", "login" and others, but
then it doesn't ask for or provide a place to enter username and password.

Can someone please shed some light on these issues?  I don't do my own DNS,
MX records etc, but I need Postfix to be able to send mail using the
smarthost.

Thanks - John