Facebook auth should include return_scopes to see which requested permissions have been granted

[seawolf42]

When the user approves FB login, they may grant all, some, or none of the scopes requested by the application. By passing "return_scopes": true as a parameter to the login URL, the data returned includes a list of scopes that were actually granted by the user.

I am happy to do the work to make this work, but I'm not entirely sure where this should go. It appears to be a parameter on the call to the AUTHORIZATION_URL, though when I add it to SOCIAL_AUTH_FACEBOOK_EXTRA_ARGUMENTS in settings it is not being picked up.

An alternate way to retrieve this info is calling the Facebook SDK (using facebook-sdk, for instance), but it seems this belongs in the authentication pipeline as that's where I am populating the database with the user's preferences and settings.

[omab]

Support added python-social-auth/social-core@4e83280

[seawolf42]

Awesome, thanks!