Webmail/Cpanel login through main website

[internetfab]

Trying to find a good way for our customers to use our website to log in to their webmail.
What I want is to just let them enter username/pass in a form field and then use POST to log them into their webmail.

Anyone know how to pass the password/username in a "secure" way? Just so it doesnt use GET..

[internetfab]

*bump*