ASP.NET Core 10 Authentication Metrics: Distinguish No Result from Failure

When every unauthorized request becomes the same dashboard line, diagnosis turns into guessing. ASP.NET Core 10 authentication metrics give me a better split: did the handler have nothing to authenticate, reject supplied credentials, or accept them? That distinction matters because a client deployment that drops credentials needs a different response from a surge of malformed or expired credentials. ASP.NET Core 10 added built-in authentication and authorization instruments to System.Diagnostics.Metrics . I can collect them without rewriting each handler, and I can lock their behavior into an offline test before wiring up a production exporter. Why one 401 hides two different problems A protected endpoint normally challenges an unauthenticated caller. The final status is 401 whether the caller sent nothing or the handler rejected what it received. The authentication duration histogram exposes the missing context through aspnetcore.authentication.result : Result What the handler reported A common interpretation none No authentication result No applicable credentials were available failure Authentication failed Supplied credentials were rejected or processing failed success A principal was created Authentication completed successfully _OTHER Another framework result Preserve it as an explicit catch-all none is a handler result, not a universal synonym for “missing Authorization header.” A policy scheme or custom handler can make a different choice. I verify the behavior of the schemes I actually deploy instead of building an alert from the label alone. Likewise, success means the handler produced an authentication ticket. Authorization can still deny that principal, so it does not promise a 2xx response. The separate aspnetcore.authentication.challenges counter answers another question: how often was a scheme challenged? Both a none result and a failure result can be followed by a challenge, so challenge count cannot replace the result split. A challenge is an authent