Hi,

Hmm.. well I can say that we have not tried that ourselves, so I’m not sure.

The current implementation relies on Eclipse Paho for the MQTT client, in there I could find: https://github.com/eclipse/paho.mqtt.java/issues/869, which pointed to https://github.com/eclipse/paho.mqtt.c/issues/808.

So for the JWT itself putting it as the password might work. But the expiry of it would be a problem by itself, since the current design has not taken into account that the password could change.

But for setting the password, see the SamplePubSubConfiguration.createMqttOverrides and the

    // User Authentication to the MQTT Broker
    builder.setAuthConfToCredentialsResolver(input -> {
      // If you have more than one broker connection, the input could be used to differentiate
      // credentials
      PubSubUsernamePasswordBrokerCredentials.Builder mqttCredentials =
          PubSubUsernamePasswordBrokerCredentials.builder();
      mqttCredentials.setUsername(brokerUsername);
      mqttCredentials.setPassword(brokerPassword);
      return mqttCredentials.build();
    });

part.

The input to the lamda is a com.prosysopc.ua.pubsub.PubSubBrokerAuthConf that you might have set for the connection conf with .setAuthConf(…). In short the resolver function set to the PubSubSystemOverrides basically “emulates” an https://reference.opcfoundation.org/Core/docs/Part14/5.4.4/#5.4.4.4 implementation (since we do not have one, so for the time being be just have a handle to “plug something here”). There are mentions of JWTs in https://reference.opcfoundation.org/v104/Core/docs/Part6/6.5.2/, though I think that was for the client-server sessionless service invocation service, but maybe the same concept can be used in PubSub (I’m not aware of anyone using the sessionless service calls, and I think we do not support those either). So it is possible that on some level the specification “supports JWTs”, just that our SDK does not.

If you can first check can you make the connection work for a short while (until the JWT expires) with the JWT as password then maybe we can add support for setting the password repeatedly (or make it so that the function is called at every mqtt connection attempt). And it might require that the Paho library updates (or that we look for some other mqtt client implementation).

P.S.
There seems to be a mention of Eclipse Paho in the link you sent so maybe we can test this ourselves at some point.