I think this may be a problem if the forms are being POSTed. As far as I know, you can't do a POST redirect, only a GET. If you're only concerned about GET, the way I've seen it done before is that all the parameters are forwarded along to the login page (usually in a session or in hidden parameters), then forwarded again to the "process" login page, and then that page redirects you back to the form submission with the parameters tacked onto the end of the URL. I don't think this is possible with POST though.
in reply to Catalyst Redirect Hints?