def __init__(self, signature, extra=None):
    '\n\n      :param signature: The signature for the authentication challenge.\n      :type signature: unicode\n      :param extra: Authentication method specific information.\n      :type extra: dict or None\n      '
    assert (type(signature) == six.text_type)
    assert ((extra is None) or (type(extra) == dict))
    Message.__init__(self)
    self.signature = signature
    self.extra = (extra or {})
:param signature: The signature for the authentication challenge.
:type signature: unicode
:param extra: Authentication method specific information.
:type extra: dict or None
def __init__(self, signature, extra=None):
    '\n\n      :param signature: The signature for the authentication challenge.\n      :type signature: unicode\n      :param extra: Authentication method specific information.\n      :type extra: dict or None\n      '
    assert (type(signature) == six.text_type)
    assert ((extra is None) or (type(extra) == dict))
    Message.__init__(self)
    self.signature = signature
    self.extra = (extra or {})