Fix dependency errors

internal/mqtt/mqtt.go

@@ -35,6 +35,11 @@ func NewClient(logger *zap.Logger, config *config.Config, csvHelper *csv.Helper)
 		}
 	})
 
+	if config.Username != "" && config.Password != "" {
+		opts.SetUsername(config.Username)
+		opts.SetPassword(config.Password)
+	}
+
 	c := mqtt.NewClient(opts)
 	if token := c.Connect(); token.Wait() && token.Error() != nil {
 		logger.Fatal("error connecting to MQTT broker", zap.Error(token.Error()))