Pass MQTT connection username and client_id to AMQP 0-9-1 message headers

[getlarge]

Is your feature request related to a problem? Please describe.

Context

A system containing a mix of MQTT and AMQP consumers and producers.
We are using RabbitMQ v3.12.13.

Problem

No information about the MQTT client is being passed to the AMQP message properties and fields.

It would be very helpful to access the client ID and username when our AMQP consumers process messages from MQTT producers to identify the producer.
I imagine the information is available since the RabbitMQ authorization methods (check resource and check topic) receive the username.
I suppose there is a reason why the information is not transferred in the AMQP payload during deliver_to_queues?

Describe the solution you'd like

In the latest publish_to_queues, the state contains the username, could we imagine setting an AMQP header containing the username and the client_id?

Do I suppose correctly that #10050 and #10051 could help achieve this?

Describe alternatives you've considered

Potential solutions

• Use MQTT v5.0 and include the user ID in the message properties
• Use a custom MQTT plugin that includes the user ID in the message properties
• Pass the MQTT client ID and user ID in the payload and/or topic

All these solutions are quite complex in our system since we don't have control over the MQTT clients' code.

Additional context

No response

[michaelklishin]

3.12.x is out of community support and the MQTT plugin in 3.13.x was substantially reworked to support MQTT 5.0.

#10050 is not MQTT-specific.

[getlarge]

Thanks for the suggestion @michaelklishin. Is there documentation or some more examples to help create such a plugin?

[michaelklishin]

The plugin above is less than 100 lines of code. There is similar plugin, rabbitmq_node_stamp, which is even smaller.

There's also an example plugin, rabbitmq_metronome.

[robertsLando]

I think we will go for that way, thanks again @michaelklishin 🙏🏼

[getlarge]

I just tried to create a channel_interceptor based on RabbitMQ 3.13.7, and unfortunately, it only intercepts messages published by AMQP producers.
The behaviour was excellent since I could use the init method to create an interceptor state based on the channel state (and extract usernames and tags).

I noticed the message_interceptor used in rabbitmq_mqtt/src/rabbit_mqtt_processor.erl, but we cannot extract auth_state, right?
Also, when trying to create a message interceptor and running the build, I received the error behaviour rabbit_message_interceptor undefined.
Is this expected?
Is it possible that: class_module(message_interceptor) -> rabbit_message_interceptor; is missing from rabbit_common/src/rabbit_registry.erl?

[robertsLando]

Just for reference:

#10051
https://groups.google.com/g/rabbitmq-users/c/gPJxxG2PGXM/m/EF2BDwpIAQAJ?pli=1

[ansd]

Passing the MQTT client ID of the publishing client to an AMQP 1.0 or AMQP 0.9.1 message of receiving clients will be possible in RabbitMQ 4.2 as explained in https://www.rabbitmq.com/docs/next/message-interceptors#mqtt-client-id and #13760