Return HTTP 403 using Authorize attribute in ASP.Net Core

After opening an issue here, it appears this actually should work…sort of.

In your Startup.Configure, if you just call app.UseMvc() and don’t register any other middleware, you will get 401 for any auth-related errors (not authenticated, authenticated but no permission).

If, however, you register one of the authentication middlewares that support it, you will correctly get 401 for unauthenticated and 403 for no permissions. For me, I used the JwtBearerMiddleware which allows authentication via a JSON Web Token. The key part is to set the AutomaticChallenge option when creating the middleware:

in Startup.Configure:

app.UseJwtBearerAuthentication(new JwtBearerOptions
{
    AutomaticAuthenticate = true,
    AutomaticChallenge = true
});
app.UseMvc();

AutomaticAuthenticate will set the ClaimsPrincipal automatically so you can access User in a controller. AutomaticChallenge allows the auth middleware to modify the response when auth errors happen (in this case setting 401 or 403 appropriately).

If you have your own authentication scheme to implement, you would inherit from AuthenticationMiddleware and AuthenticationHandler similar to how the JWT implementation works.