It looks like your seedlings example is a bit outdated, when setting up an application, Facebook now asks for a "Secure Canvas URL" (https ) as well as a regular one. This is so, if someone has the "Secure Browsing (https)" turned on on their account settings, they get all pages on facebook prefixed with an "https". So if a user like that tries to use a facebook app, that would also need to be https.
I tried faking it, by changing the Canvas URL produced by PlayerIO, from an http to https, but i get a nasty error message on facebook:
"Secure Connection Failed"
SSL received a record that exceeded the maximum permissible length.
(Error code: ssl_error_rx_record_too_long)
Any ideas ?
