},
... Exclusive('social', 'auth', msg=msg):{
...     Required('social_network'): str,
...     Required('token'): str
...     }
... })

>>> with raises(er.MultipleInvalid, "Please, use only one type of authentication at the same time. @ data[<auth>]"):
...     schema({'classic': {'email': 'foo@example.com', 'password': 'bar'},
...             'social': {'social_network': 'barfoo', 'token': 'tEMp'}})
c