The actual workflow here is an open standard, but I'm having a hard time understanding why sites won't just require that you use Mediators/Issuers that were written by one of the big tech companies and then block everything else.
Not saying that will absolutely be the case, I'm just saying that I don't understand why I shouldn't be concerned -- I've seen these exact arguments get used in the past for systems that absolutely shut out independent browser/hardware/OS/ROM development.
I mean... CAPTCHA is effectively an Open Standard, even if it doesn't have a draft that I'm aware of. But that doesn't mean much when so much of how it works is rolled up in an unstandardized implementation and when website operators are ultimately in charge of choosing CAPTCHA providers, not users. Is the same thing going to happen with PATs?