Perform authentication with Twitter and return a client instance to communicate with Twitter

    :param config: ResponseBot config
    :type config: :class:`~responsebot.utils.config_utils.ResponseBotConfig`
    :return: client instance to execute twitter action
    :rtype: :class:`~responsebot.responsebot_client.ResponseBotClient`
    :raises: :class:`~responsebot.common.exceptions.AuthenticationError`: If failed to authenticate
    :raises: :class:`~responsebot.common.exceptions.APIQuotaError`: If API call rate reached limit

def auth(config):
    """
    Perform authentication with Twitter and return a client instance to communicate with Twitter

    :param config: ResponseBot config
    :type config: :class:`~responsebot.utils.config_utils.ResponseBotConfig`
    :return: client instance to execute twitter action
    :rtype: :class:`~responsebot.responsebot_client.ResponseBotClient`
    :raises: :class:`~responsebot.common.exceptions.AuthenticationError`: If failed to authenticate
    :raises: :class:`~responsebot.common.exceptions.APIQuotaError`: If API call rate reached limit
    """
    auth = tweepy.OAuthHandler(config.get('consumer_key'), config.get('consumer_secret'))
    auth.set_access_token(config.get('token_key'), config.get('token_secret'))

    api = tweepy.API(auth)
    try:
        api.verify_credentials()
    except RateLimitError as e:
        raise APIQuotaError(e.args[0][0]['message'])
    except TweepError as e:
        raise AuthenticationError(e.args[0][0]['message'])
    else:
        logging.info('Successfully authenticated as %s' % api.me().screen_name)

        return ResponseBotClient(config=config, client=api)