Compatibility with Social Auth 4.x

Created a merge request. Note that it's against the current 8.x-3.x branch which contains the latest code.

Ideally, a new 4.0.x branch should be created to be consistent with the social_api and social_auth modules and the MR changed to target it.

Similarly, for consistency, once approved, a new 4.0.0 release should be created.

Created 4.0 branch

Automatically closed - issue fixed for 2 weeks with no activity.