redirect_to("url") with post?

Ben Blakley wrote:

Is this the only way to post/pass variables when redirecting a request to another server?

redirect_to("http://whatever.com?postme=this")

I'd like to be able to hide the variables instead of sending them in the URL. For example, when logged into Basecamp you can view/create Writeboards without logging into Writeboard even though you are redirected to a different server/domain. It doesn't appear to me that your login or authentication info is being passed from Basecamp to Writeboard in the URL. Does anyone know how this is done? Thanks!

According to http://ppewww.ph.gla.ac.uk/~flavell/www/post-redirect.html
you can control whether a POST redirects as a GET or a POST by changing
the response status code.

But if you don't need to do stuff in your action prior to redirecting
you can just post directly to the external site from a form on your
page.