Best way to diagnose HTTP 401

[raffaeler]

The new templates includes IdentityServer in the pipeline and it is not always trivial to understand the reasons for a 401.
I tried the new .NET 5 react template and, even without modifying the default code, after 24 hours the WeatherForecastController cannot be accessed anymore.
In the browser I can see the code retrieving a valid bearer token, but the following GET for the weather data fails as "invalid json" and HTTP 401.
Changing the logging level to "Trace" did not help either.