must call before bind

def set_client_key(self, zmq_socket, client_secret_key_path, server_public_key_path):
        '''must call before bind'''
        load_and_set_key(zmq_socket, client_secret_key_path)
        server_public, _ = zmq.auth.load_certificate(server_public_key_path)
        zmq_socket.curve_serverkey = server_public