def allow_relation(self, obj1, obj2, **hints):
        if obj1._meta.app_label == 'auth' or obj2._meta.app_label == 'auth':
            return True
        return None
Allow any relation if a model in Auth is involved
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/tests/regressiontests/multiple_database/tests.py/AuthRouter.allow_relation