Inlcude client id in notfication

[PatersonKopp]

Dear all,
I'm tring to build a small service using this your rumqttd packages to ingest messages from IoT devices into a time series database. For this, I need to know the ID of the client that sent the message.
However, the "Notification" structure only includes the topic, payload, and a few other fields, but not the client ID.

I considered adding the client ID to the topic, but since I can only control which clients are allowed to connect (and not which clients are allowed to publish to specific topics), any device could publish messages for others.

Is there a way to access the client ID within the broker per incoming message, or a different approach to solve this? Any advice would be appreciated!