'Request challenges.
:param .messages.Identifier identifier: Identifier to be challenged.
:param str new_authzr_uri: Deprecated. Do not use.
:returns: Authorization Resource.
:rtype: `.AuthorizationResource`'

def request_challenges(self, identifier, new_authzr_uri=None):

    if (new_authzr_uri is not None):
        logger.debug('request_challenges    with    new_authzr_uri    deprecated.')
    new_authz = messages.NewAuthorization(identifier=identifier)
    response = self.net.post(self.directory.new_authz, new_authz)
    assert (response.status_code == http_client.CREATED)
    return self._authzr_from_response(response, identifier)
