Extension for ASP.NET Core Startup to return 401 on unauthorized API calls

startup_extension.cs

public static IApplicationBuilder Use401ForUnauthorizedApiCalls(this IApplicationBuilder app)
{
    app.Use(async (context, next) =>
    {
        if (context.Request.Path.Value.Contains("/api") &&
            (context.User == null ||
            context.User.Identity == null ||
            !context.User.Identity.IsAuthenticated))
        {
            context.Response.StatusCode = 401;
            return;
        }

        await next();
    });

    return app;
}