A couple of years ago or so Heroku and Facebook teamed up to make creating Facebook apps a doddle. Indeed one can do so with a few clicks from the app creation centre in Facebook if you already have a Heroku account.
Here are pretty comprehensive instructions from Heroku on how to do this, and I can attest that it all works well.
I've added to this setup with a staging instance for team testing purposes using the facility Heroku has for managing different environments by pushing to different remotes. See this handy guide for full details.
To create a staging branch called
heroku create --remote staging
And to add Facebook app credentials for the staging version of your app just do:
heroku config:add FACEBOOK_APP_ID=123456 FACEBOOK_SECRET=789102323etc --remote staging