Constrained Application Protocol (en.wikipedia.org)

I encountered CoAP when reading about the DDoS Open Threat Signaling protocol [1], unfortunately it doesn't look like any of the commercial anti-DDoS services are using that standard.

[1]: https://www.rfc-editor.org/rfc/rfc8811

This looked really cool, but I completely forgot it existed. The open source IoT world doesn't seem to use it at all