Pass-thru authentication between 2 or more sites

[Oleg Ogurok]

Hi all,

I was wondering if there was a nice way to implement authentication between
several sites.
I currently have 2 web servers, one for the main site (e.g. www.main.com)
and the other one for the web forum (e.g. www.forum.com). After a person
logs into the main site, he at some point may be redirected to the forum
site through
Response.Redirect("www.forum.com?username=foo&password=bar&thread=333");
Sinse it's unwise to pass the password in clear text, how would I encrypt
it? Is there a better solution?
Thanks,

Oleg.