I think it just problem this app, but it doesn't work:(
facebook app error
I had to hit errors until I figured out that I need to include this URL on the OAuth settings:
That url is not documented anywhere as far as I could see. I even dug around here a bit (maybe not long enough). So I would think the instructions should be documented somewhere so we don't have to guess these URLs.
Turns out that Twitter and Google do have instructions.