Extracted logout to the login service so the logic can be shared instead
of re-implemented at each stage. For this, the SocialAuthService was
split so the driver management is in its own class, so it can be used
elsewhere without use (or circular dependencies) of the
SocialAuthService.
During review of #4467
- Updated existing tests now affected by my-account changes.
- Updated some existing tests to more accuractly check the scenario.
- Updated some code styling in SocialController.
- Fixed redirects for social account flows to fit my-account.
- Added test for social account attaching.
- Added test for api token redirect handling.
