What’s buried in this presentation is Passkey - here’s an excerpt:

> This new feature stores a new type of credential, called a "passkey", in your iCloud Keychain. Passkeys are WebAuthn credentials with the amazing security that the standard provides combined with the usability of being backed up, synced, and working on all of your devices. We’re storing them in iCloud Keychain. Just like everything else in your iCloud Keychain, they’re end-to-end encrypted, so not even Apple can read them.