Create a new login
        :param user: AuthUser
        :param provider: str - ie: facebook, twitter, ...
        :param federated_id: str - an id associated to provider
        :return:

def new(cls, user, provider, federated_id):
        """
        Create a new login
        :param user: AuthUser
        :param provider: str - ie: facebook, twitter, ...
        :param federated_id: str - an id associated to provider
        :return:
        """
        if cls.get_user(provider, federated_id):
            raise exceptions.AuthError("Federation already")

        return cls.create(user_id=user.id,
                          provider=provider,
                          federated_id=federated_id)