WebAuthn Level 3 § 5.1.3 Step 22 Item 4 states the steps a user agent MUST follow when "conditional" mediation is used in conjunction with required user verification: Let userVerification be the effective user verification requirement for credential creation, a Boolean value, as follows. If pkOptions.authenticatorSelection.userVerification is set to required If options.mediation is set to conditional and user verification cannot be collected during the ceremony, throw a ConstraintError DOMException. Let userVerification be true. On my iPhone 15 Pro Max running iOS 18.5, Safari + Passwords does not exhibit this behavior; instead an error is not reported and user verification is not performed (i.e., the UV bit is 0). Per the spec this results in a registration ceremony failure on the server which is made all the more "annoying" since the credential was created in Passwords forcing a user to then delete the credential. : If the Relying Party requires user verification for this registration, verify that the UV bit of the flags in authData is set. In contrast when I use Google Password Manager + Chrome on a Samsung Galaxy S24 running Android 15, user verification is enforced and the UV bit is 1. Either the UV bit should be 1 after enforcing user verification or an error should be thrown since user verification cannot be performed.

WebAuthn Level 3 § 6.3.2 Step 2 states the authenticator must : Check if at least one of the specified combinations of PublicKeyCredentialType and cryptographic parameters in credTypesAndPubKeyAlgs is supported. If not, return an error code equivalent to "NotSupportedError" and terminate the operation. On my iPhone 15 Pro Max running iOS 18.5, Safari + Passwords does not exhibit this behavior; instead an error is not reported and an ES256 credential is created when an RP passes a non-empty sequence that does not contain {"type":"public-key","alg":-7} (e.g., [{"type":"public-key","alg":-8}]). When I use Chromium 138.0.7204.92 on my laptop running Arch Linux in conjunction with the Passwords app (connected via the "hybrid" protocol), a credential is not created and instead an error is reported per the spec.

When creating a passkey with the PRF extension on an iPhone 15 Pro Max using Safari on iOS 18.4.1, PublicKeyCredential.getClientExtensionResults reports true; however there is no hmac-secret extension in the authenticator data as required by WebAuthn Level 3.