From October 1st all Facebook apps must have SSL certificates in order to function well. Since we have a lot of apps that are used on Facebook pages as page tabs we bumped into a problem where on HTTP the app tabs were displayed as expected while on HTTPS (via SSL) the page tab application was blank. Facebook was not even making a request to the sever via HTTPS. The solution of the problem was much simpler than any of us expected. Here are the old Facebook application settings:
We were using relative tab URL and secure tab URL. While this configuration works well without SSL, on HTTPS was not. Another strange thing was when we accessed the Facebook app canvas via app.facebook.com/app.. the app was loading on HTTP and HTTPS. Changing the page tab URL and the secure page tab URL to an absolute URL fixed the problem immediately. Here are the new application settings.
Also to avoid any other errors, please make sure that when showing the app via SSL, you do not have any mixed content, everything must load from HTTPS.