LG-8071: Add logging for WebAuthn frontend error reasons

[aduth]

🎫 Ticket

LG-8071

🛠 Summary of changes

Enhances WebAuthn verification to ensure that errors occurring in the front-end are logged as part of the back-end verification.

Previously, the frontend error message was being passed as part of the form submission, but was only used as part of a condition considering whether to validate the assertion response. With these changes, the error is now included in the logged error details.

This changes the specific string being logged from using the full error message to the error name, which avoids differences in error messages between browsers.

For example, a cancelled authentication...

• ...in Chrome:
  • error.name: NotAllowedError
  • error.message: The operation either timed out or was not allowed. See: https://www.w3.org/TR/webauthn-2/#sctn-privacy-considerations-client.
• ...in Safari:
  • error.name: NotAllowedError
  • error.message: This request has been cancelled by the user.

Draft while I work to enhance test coverage

📜 Testing Plan

1. Configure an account with Security Key or Face/Touch Unlock
2. Tail logs (tail -F log/events.log | jq .)
3. Sign in, but cancel when prompted for Security Key or Face/Touch Unlock
4. Observe event "Multi-Factor Authentication" with errors including webauthn_error: ['NotAllowedError']

[zachmargolis]

LGTM