Allow anonymous MQTT broker connections

src/main.cpp

@@ -296,9 +296,9 @@ static void mqttSubscribe() {
 }
 
 static bool mqttConnect() {
-  if (!mqttCfg.enabled || strlen(mqttCfg.host) == 0 || strlen(mqttCfg.user) == 0 || strlen(mqttCfg.pass) == 0) {
-    Serial.printf("[MQTT] connect skipped en=%d host=%d user=%d pass=%d\n",
-      mqttCfg.enabled, strlen(mqttCfg.host) > 0, strlen(mqttCfg.user) > 0, strlen(mqttCfg.pass) > 0);
+  if (!mqttCfg.enabled || strlen(mqttCfg.host) == 0) {
+    Serial.printf("[MQTT] connect skipped en=%d host=%d\n",
+      mqttCfg.enabled, strlen(mqttCfg.host) > 0);
     return false;
   }
 
@@ -316,8 +316,13 @@ static bool mqttConnect() {
   mqttClient.setCallback(mqttCallback);
   mqttClient.setBufferSize(1024);
 
+  // Pass NULL for empty credentials so the broker treats it as an anonymous
+  // connection rather than an empty-string login (which some brokers reject).
+  const char* user = strlen(mqttCfg.user) > 0 ? mqttCfg.user : nullptr;
+  const char* pass = strlen(mqttCfg.pass) > 0 ? mqttCfg.pass : nullptr;
+
   Serial.printf("[MQTT] connecting to %s:%d as %s\n", mqttCfg.host, mqttCfg.port, clientId);
-  bool ok = mqttClient.connect(clientId, mqttCfg.user, mqttCfg.pass,
+  bool ok = mqttClient.connect(clientId, user, pass,
                                statusTopic, 0, true, "online: false");
 
   if (ok) {
@@ -334,7 +339,7 @@ static bool mqttConnect() {
 }
 
 static void mqttLoop() {
-  if (!mqttCfg.enabled || strlen(mqttCfg.host) == 0 || strlen(mqttCfg.user) == 0 || strlen(mqttCfg.pass) == 0) return;
+  if (!mqttCfg.enabled || strlen(mqttCfg.host) == 0) return;
 
   if (!mqttClient.connected()) {
     unsigned long now = millis();