MQTT Client ID and topic prefix should match when is_name_add_mac_suffix_enabled() is true

[kaechele]

Component name

mqtt

Link to component documentation on our website

https://esphome.io/components/mqtt/

Describe the enhancement

When using name_add_mac_suffix: true the automatically generated MQTT client ID and topic prefix should match.
Right now the client ID will be <APP_NAME>-<MAC> and the topic prefix will be <APP_NAME>.
To illustrate, take a device with MAC address 12:34:56:78:90:AB that has the following settings:

esphome:
  name: mydevice
  name_add_mac_suffix: true

Resulting MQTT Client ID: mydevice-7890ab-1234567890ab
Resulting Topic Prefix: mydevice-7890ab

Ideally, both the client ID and the topic prefix would be the same.

Use cases

Mosquitto allows restricting access to topics based on dynamic ACLs. Subscriptions to topics can be limited based on topic patterns. Two variables are available there for substitution %u for the username and %c for the client ID.

Imagine a scenario where you are deploying a number of similar ESPHome devices with MQTT. You create one common build with name_add_mac_suffix enabled to be able to tell them apart without needing a separate build for each device. Due to the single common build you only have one set of MQTT credentials hardcoded into the build, so identifying nodes by username is not possible.

To enhance security you now want to limit devices to only be able to subscribe and publish to topics that are relevant to itself.

Using the dynamic security plugin you can create the ACL pattern '%c/#' meaning the device can access any topics that start with its client ID.
But when the Client ID and topic prefix being differs you cannot do this.
This is only problematic when using name_add_mac_suffix because mqtt.client_id and mqtt.topic_prefix don't accept lambdas, so you have no way of pulling either the mac address or App.get_name() during runtime to create unique IDs.

Anything else?

This issue would be solved if either:

1. MQTT client ID and topic prefix were the same when name_add_mac_suffix is used OR
2. mqtt.client_id and mqtt.topic_prefix accepted lambdas

[github-actions[bot]]

🏷️ I've automatically added the component: mqtt label to help categorize this feature request.