Re-Posting a Form


I have a third-party service who wants me to host a data collection
form that posts to their server. However, I want to do validation and
if all works properly, then issue an http post to their server with
the proper request variables set as though the form had just been
filled out.

So far, it’s kind of like this:

index : shows form
signup : the ‘show’ method. if all is well, should form the request
vars and post to remote server, else render index

Is there a best practice for stuffing a request and posting to some
arbitrary URL?