Registration set no authenticatorSelection, so the browser offered the
passkey-manager 'save passkey' flow (Bitwarden) instead of prompting for the
YubiKey. Now request a cross-platform, non-resident, presence-only credential:
authenticatorAttachment=cross-platform (roaming key, not a platform/manager
passkey), residentKey=discouraged (non-discoverable second factor — what keeps
passkey managers out), userVerification=discouraged (single touch, no PIN).
Login assertion also uses discouraged so it is: insert key, one tap, done.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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