Using multiple facebook apps with facebooker

Facebooker with multiple facebook apps

Multiple facebook apps on one facebooker-powered Rails app.  This
should be backwards compatible. For adding an app:

development:
  api_key: 963285923uj23j8rj23j932
  secret_key: fj329jf932jf9329t939hg239t
  canvas_page_name: mainapp
  pretty_errors: true
  set_asset_host_to_callback_url: true
  callback_url: http://www.host.com
  alternative_keys:
    "2a9hf29hf29f2h2f9hf29":
      secret_key: jfh92h3f932h9f329f9329hf
      canvas_page_name: alternativeapp
      pretty_errors: true
      set_asset_host_to_callback_url: true
      callback_url: http://www.host.com

You can load up as many alternative_keys as desired. Really,
the "main" config has nothing special besides being the config
initialized when Rails is started. Inside a given request,
the whole app.call is wrapped in the same block regardless of
if the api_key is the main or an alternative app.

Offline tasks are a little more messy- you need to know what
app you'd like to fire something for. Once you know that,
things get cleaner:

gift = Gift.find :first
Facebooker.with_application(gift.on_app_api_key) do
  FacebookerNotifier.deliver_new_gift_notification(gift)
end

As you can see in the tests, anything inside the block uses
the configuration for that api_key. Once the block ends, the
previous config replaces it.