Facebook canvas app not loading, scraper shows correct document

Question

I've created a FB application, hosted on Heroku. The app is written in Ruby.

1. The app used to load correctly inside facebook iframe.
2. Now, if I open the app through app.facebook.com/app_namespace, an empty screen is shown. When I have enabled exception trace, it now shows as if the access_token for graph koala object is nil.
3. If I open Canvas URL, e.g. the "direct" URL everything works fine, but I have to first call direct authroization on facebook through "/auth/facebook".
4. The iframe now shows koala "Unsupported get method", but through debugging it is evident that access_token obtained from graph is nil.
5. Behavior is the same for generated test users as well as developer users.

Already tried:

1. I've tried to debug the Canvas URL through online FB debugger, and Scraper seems to see correct HTML.
2. Try to reauthorize the app, to no avail.

Answer 1

By default Sinatra uses rack-protection to set the X-Frame_Options header. It looks like this is what is causing your problems.

You can disable it with this line in your application:

set :protection, :except => :frame_options