This morning I worked on the websub.rocks test suite, and wrote a helper library for creating a WebSub client.
The test suite now keeps track of some basic stats when you use the publisher tests, which will help me keep track of which spec features are implemented.
I released a WebSub client as a Composer library: https://github.com/aaronpk/p3k-websub The package has a few helper functions for discovering hub for a topic, and sending the subscription request. Hopefully it is helpful for people writing WebSub consumers! I know I'll be using it in several projects soon!