off-topic question about secure proxy authentication

[Gaston Franco]

Hi!
the following question is a little off-topic, but as it is about
security, maybe somebody in this list can help me and i think the
answer could be useful for many of us.

I have a network with a iptables firewall and a machine with squid-proxy
behind. The internal users need to authenticate to the proxy.
Everything is working fine. But now, I´d like to make the authentication
process more robust, without having to send the user password in cleartext
using the HTTP basic authentication method. I´ve tried implementing HTTP
digest authentication method, but i´d a problem with netscape 4.x not
supporting this method.
Does anybody know how can I replace this method with something more secure?

I´m trying to avoid using cleartext passwords on the net, and this is the
last service I´ve to change.

TIA .