Where is rumqttd documentation?

[MightyPork]

Hi, I've been using rumqttc for a couple years. Today I wanted to look at rumqttd but can't find any documentation and the examples look incomplete and/or broken. Is there something I can read to understand the different concepts of the broker, like bridge, segments, metrics, alerts ...? Thanks

What I want to do is hook into the broker and receive events when a client joins, leaves, subscribes, publishes something etc. The goal is to have a sort of "MQTT proxy" where I can track what clients want and spoof the messages when the real broker is offline (mqtt is used to distribute config).