The attestation anti-feature which is part of the spec. And the portability feature which is conspicuously not. The former makes the enforcement of the later possible.
The attestation is part of the webauthn spec, and it's up to the relying party to decide whether or not to use it. The whole reason it's there is to give some contexts the ability to narrow their users down to specific webauthn storage implementations (which is useful in some corporate / gov contexts).
Are there any examples of any widely-used sites that are enforcing attestation?
- Cloudflare had a "captcha" POC called "Cryptographic Attestation of Personhood" where you need to use a FIDO-approved token. It's reusing U2F just for the attestation part only. I don't think it ever go to production as most people don't have a token (but perhaps in the future hardware-locked passkey may serve as one...)
- Okta do have an option to enforce attestation. By default it is off, but in my Okta production I can limit the list to FIDO-approved vendor only, or to even a subset of them. They also have a beta feature flag for blocking Passkeys but allowing physical keys (which they do not guarantee success)
OK, so you gave two examples of systems that do NOT enforce attestation (one that is not in production, one that has an option to enforce attestation but is not apparently in use).
Are there any widely-used sites that actually enforce attestation?
People already do have issues with e.g. banking apps on mobile devices requiring OS attestation, so we can expect that once they know they can do the same for the most of their web clients (so probably once most people have moved onto Windows 11 which requires a TPM), they will.
It’s absurd, really. Attestation is clearly a feature intended for high security environments, where you want to ensure all employees use their corporate hardware authenticators and those only, yet people act like it’s big techs secret, evil mind control back door.
Given the chance, why wouldn't companies abuse that feature like every single anti-user feature in the history of them? Surely this time it will be different?
It's only a matter of time when it's this easy. Some essential service, most likely a bank, will inevitably turn it on in the future. And it only takes one of those to make all freedom respecting providers non-viable for someone. For our safety, of course. :)