Secure Squid

Hi,

that's my system: I've an exchange2003server and I use Squid 3.0 to
access Outlook Web Access with SSL. Everything works! Now my question:
We've few (5) employees which use OWA and I want to secure that
connection. I heard something about proxie_auth I thought about
RSA-SecurID tokens. but that is to expensive for now. Do you've ideas
for a solution how to secure squid effectively.

Sry I don't know why but I think my text looks bad :-) I'm not
english.. :-)

Thanks

me