1. Prove the human-ness of an author... 2. ...without grossly encroaching on their privacy. 3. Ensure that the author isn't passing off AI-generated material as their own.
We'll leave out the "don't let AI models train on my data" part for now.
Whatever solution we come up with, if any, will necessarily be mired in the politics of privacy, anonymity, and/or DRM. In any case, it's hard to conceive of a world where the human web returns as we once knew it.