def METHOD_NAME(
        self, client_id, auth_flow, user_name, password, device_key,
        challenge_name, error_code=None):
    expected_params = {
        'ClientId': client_id, 'AuthFlow': auth_flow,
        'AuthParameters': {
            'USERNAME': user_name, 'PASSWORD': password, 'DEVICE_KEY': device_key}}
    response = {'ChallengeName': challenge_name}
    self._stub_bifurcator(
        'initiate_auth', expected_params, response, error_code=error_code)