ASPNETCORE ConfigureServices does not run

Question

I follow the Microsoft document to implement the policy-based authorization in my web service but the function "ConfigureServices" does not run. Please let me know if I have something missing.

Startup.cs

using Microsoft.Owin;
using Owin;
using Microsoft.AspNetCore.Authorization;
using Microsoft.Extensions.DependencyInjection;

[assembly: OwinStartupAttribute(typeof(WebApplication1.Startup))]
namespace WebApplication1
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureAuth(app);
        }

        public void ConfigureServices(IServiceCollection services)
        {       
            //Some codes here...
        }
    }
}