feat(webauthn): scrub attestation for attestation=none conveyance#284
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WebAuthn L3 §5.4.1 requires the platform to anonymise the attestation object when the relying party requests attestation conveyance "none": replace fmt with "none", attStmt with an empty map, and zero the AAGUID in the authenticator data. libwebauthn parsed the conveyance preference but discarded it, forwarding the authenticator's real format, attStmt, and AAGUID verbatim. This honours the preference at response assembly time. The WebAuthn IDL default of "none" is applied at the IDL boundary, so JSON requests that omit attestation are scrubbed too. Requests built directly with attestation None pass through.
AlfioEmanueleFresta
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When a relying party requests no attestation, the client now removes the attestation statement and zeroes the AAGUID before returning the credential, rather than forwarding the authenticator attestation verbatim. This honors the requested conveyance and avoids disclosing identifying device information for a privacy-preferring registration. Requests that ask for direct or indirect attestation are unchanged.