User                 string         `json:"username"`
	Password             string         `json:"password"`
	MaxReconnectInterval time.Duration  `json:"reconnectInterval"`
	KeepAlive            time.Duration  `json:"keepAliveInterval"`
	RootCAs              *x509.CertPool `json:"-"`
	QueueDir             string         `json:"queueDir"`
	QueueLimit           uint64         `json:"queueLimit"`
}

// Validate MQTTArgs fields

		if err != nil {
			return nil, err
		}

		keepAliveIntervalEnv := target.EnvMQTTKeepAliveInterval
		if k != config.Default {
			keepAliveIntervalEnv = keepAliveIntervalEnv + config.Default + k
		}
		keepAliveInterval, err := time.ParseDuration(env.Get(keepAliveIntervalEnv,
			kv.Get(target.MqttKeepAliveInterval)))
		if err != nil {
			return nil, err
		}

		queueLimitEnv := target.EnvMQTTQueueLimit