How to solve the problem of username and password authentication failure when connecting to local EMQX using Eclipse Paho?

Eclipse Paho MQTTAsyncClient connection to local EMQX username password authentication solution

This document explains the solution to the problem of failing username and password authentication when connecting to local EMQX MQTT Broker using Java and Eclipse Paho's MQTTAsyncClient library.

Problem description

When using the org.eclipse.paho.client.mqttv3 library to connect to local EMQX (configured for built-in database password authentication, password encryption is plain, salt-disabled), the connection will still fail and MqttSecurityException: 错误的用户名或密码exception is thrown. The MQTTX client test connection was successful. The Java code is as follows:

 String brokerUrl = "tcp://127.0.0.1:1883";
MqttAsyncClient mqttClient = new MqttAsyncClient(brokerUrl, "test");

MqttConnectOptions connOpts = new MqttConnectOptions();
connOpts.setUserName("emqx_test");
connOpts.setPassword("emqx_test_password".toCharArray());
connOpts.setServerURIs(new String[] { brokerUrl });
connOpts.setCleanSession(true);

mqttClient.connect(connOpts, connStatus); // The problem lies

The callback function onFailure returns reason_code_failed_authentication error code. When EMQX's built-in database authentication is disabled, the connection is successful, but the EMQX console shows that the username is missing.

Solution

The problem is the line of code mqttClient.connect(connOpts, connStatus); In order to correctly authenticate username and password, it needs to be modified to:

 mqttClient.connect(connOpts, null, connStatus);

Setting the second parameter null can solve the authentication failure problem. After modification, the connection is successful and the username authentication takes effect.

Through the above adjustments, the user name and password authentication failure can be solved when the Eclipse Paho MQTTAsyncClient is connected to local EMQX.

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