WebauthnService builds creation/request options (rpId = active domain, ES256/RS256,
attestation none, exclude/allow lists) via web-auth/webauthn-lib v5, stores the
challenge in the session, and verifies attestation/assertion responses (allowed
origin = https://<rpId>, sign-count tracked). Option building + serialization are
unit-tested; the cryptographic verify path is browser-verified on a domain host.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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