Support "Legacy Authentication" Setting Failure Response

[AdrianJSClark]

Once iRacing rolls out two factor authentication (2FA), which is currently due to happen the week of 30 Sep 2024 to 4 Oct 2024, authentication to the /auth endpoint will fail unless the user account has enabled the "Legacy Authentication" option in their account settings.

The failure will be an HTTP 401 response with the following content:

{"error": "access_denied", "error_description": "legacy authorization refused"}

Support this response, log the reason authentication failed, and throw an appropriate exception.