Warning:
For some special and stupid reasons, the 8.x-1.0 just support social_auth:^1.0.
8.x-2.x will support social_auth:^2.0,But the development hasn't started. Will be very glad to accept help of issues and patches.
Social auth facebook api
This module provide a endpoint to login to drupal by facebook's access_token
And this module use the same logic of social_auth_facebook