CVE-2026-107808: Nginx UI: Authentication bypass: password login does not enforce a passkey-only second factor (2FA bypass)

nginx-ui supports two second-factor methods — TOTP (OTP) and WebAuthn passkeys — and reports an account as 2FA-enabled when either is configured. However, the password login endpoint (POST /api/login) only enforces a second factor when a TOTP secret is present. An account that has registered a passkey but no TOTP is logged in after password verification alone — the passkey is never requested. This silently downgrades a passkey-protected account to single-factor (password-only) authentication.