async def METHOD_NAME(self):
    """
    An async callback returning a :class:`str` ID/Access Token to be sent to
    the Kafka client. In case where a synchoronous callback is needed,
    implementations like following can be used:
    .. code-block:: python
        from aiokafka.abc import AbstractTokenProvider
        class CustomTokenProvider(AbstractTokenProvider):
            async def token(self):
                return await asyncio.get_running_loop().run_in_executor(
                    None, self._token)
            def _token(self):
                # The actual synchoronous token callback.
    """
    pass