Python-social-auth OAUTH1a login has been fails with an error
Direct assignment to the forward side of a many-to-many set is prohibited. Use groups.set() instead.
Workaround in upstream is to add following line to settings.py per python-social-auth ticket.
SOCIAL_AUTH_PROTECTED_USER_FIELDS = ['groups']
The workaround is added to the Help:Toolforge/My first Django OAuth tool tutorial, but i made and ticket for documenting the bug.