protect_from_forgery

I am a newbie to Rails, coming from a PHP shop, so please excuse my
ignorance.

I have to applications. A Codeigniter PHP app and a Rails 3.0 app. The
rails app makes paypal api calls and the php app makes curl post calls
to the rails app with information from a shopping cart.

How can I make this work with protect_from_forgery? I basically want to
pass my own auth token from the php app (or any 3rd party app for that
matter) to my rails app so that it knows its ok to proceed.

Thanks in advance for all help!