Я работаю над добавлением ролей администратора и обычного пользователя ASP. NET Core MVC

Question

Это мой файл startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using DustBusters1.Models;
using Microsoft.Extensions.Configuration;
using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Identity;

namespace DustBusters1
{
    public class Startup
    {
        IConfigurationRoot Configuration;

        public Startup(IWebHostEnvironment env)
        {
            Configuration = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json").Build();
        }

        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            //services.AddTransient<IProductRepository, FakeProductRepository>();
            services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
            services.AddTransient<IProductRepository, EFProductRepository>();
            services.AddScoped<Cart>(sp => SessionCart.GetCart(sp));
            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
            services.AddTransient<IOrderRepository, EFOrderRepository>();
            services.AddIdentity<AppUser, IdentityRole<Guid>>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();
            services.AddMvc(options => options.EnableEndpointRouting = false)
.AddNewtonsoftJson();
            services.AddMemoryCache();
            services.AddSession();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory)
        {
            app.UseDeveloperExceptionPage();
            app.UseStatusCodePages();
            app.UseStaticFiles();
            app.UseAuthentication();
            app.UseSession();
            app.UseMvc(routes => {
                routes.MapRoute(
                name: null,
                template: "{category}/Page{page:int}",
                defaults: new { controller = "Product", action = "List" }
                );
                routes.MapRoute(
                name: null,
                template: "Page{page:int}",
                defaults: new { controller = "Product", action = "List", page = 1 }
                );
                routes.MapRoute(
                name: null,
                template: "{category}",
                defaults: new { controller = "Product", action = "List", page = 1 }
                );
                routes.MapRoute(
                name: null,
                template: "",
                defaults: new { controller = "Product", action = "List", page = 1 });
                routes.MapRoute(name: null, template: "{controller}/{action}/{id?}");
            });
        }
    }
}

Это мой AdminController.cs

using Microsoft.AspNetCore.Mvc;
using DustBusters1.Models;
using System.Linq;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace DustBusters1.Controllers
{
    [Authorize]
    public class AdminController : Controller
    {
        private readonly RoleManager<IdentityRole> RoleManager;
        private IProductRepository repository;

        public AdminController(IProductRepository repo, RoleManager<IdentityRole> RoleManager)
        {
            repository = repo;
            this.RoleManager = RoleManager;
        }

        [HttpGet]
        public IActionResult CreateRole()
        {
            return View();
        }

        public ViewResult Index() => View(repository.Products);
        public ViewResult Edit(int productId) => View(repository.Products.FirstOrDefault(p => p.ProductID == productId));

        [HttpPost]
        public IActionResult Edit(Product product)
        {
            if (ModelState.IsValid)
            {
                repository.SaveProduct(product);
                TempData["message"] = $"{product.Name} has been saved";
                return RedirectToAction("Index");
            }
            else
            {
                // there is something wrong with the data values
                return View(product);
            }
        }

        public ViewResult Create() => View("Edit", new Product());

        [HttpPost]
        public IActionResult Delete(int productId)
        {
            Product deletedProduct = repository.DeleteProduct(productId);

            if (deletedProduct != null)
            {
                TempData["message"] = $"{deletedProduct.Name} was deleted";
            }

            return RedirectToAction("Index");
        }
    }
}

Я получаю эту ошибку и понятия не имею, что мне делать искать вокруг, и я не знаю, что я делаю неправильно. Любой, кто может дать мне совет или отзыв о том, как это исправить. Спасибо.

InvalidOperationException: невозможно разрешить службу для типа 'Microsoft.AspNetCore.Identity.RoleManager`1 [Microsoft.AspNetCore.Identity.IdentityRole]' при попытке активировать DustBusters1.Controllers.AdminController '