The Diagnostic Utility makes a simple request to get the metadata of the OAuth issuer URL specified in the WebAPISettings.json settings file.
Authentication server [URL] could not be reached
Response code 404 was returned when trying to reach the specified URL.
Authentication server [URL] is not a valid API
The URL specified is not a valid API URL.
Could not determine status of authentication server [URL]
A response code other than 200 or 404 was returned when trying to reach the URL.