Capybara and a post request

Hi there!

In my app I have an entry page that is called with an post-request from another site. This post-request contains a parameter called key and is used for an app authorisation of that other site.

How can I simulate such a behaviour in respect and capybara?

In the moment I have a controller and action that serves me a Form where I fill in the key and click submit via capybara. But I think this is a little bit hacky, also this form is not necessary for the app itself. I would like to remove this overhead if possible.