in reply to Go to Website that requires Login

I don't think you can. You could provide a proxy on your site, that does the actual request on the other site and passes the result back to your browser.

There has been a user here, ant9000, who did something for Perlmonks, for a Ajax based Chatterbox client. The proxy is still alive: http://www.netwise.it/xml/perlmonks/.

Since then, this user has disappeared.