Program.cs

using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using platform.Models;
using platform.Models.Account;
using platform.Services.Email;

namespace platform
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // add services
            builder.Services.AddControllersWithViews();
            ConfigureServices(builder.Services, builder.Configuration);
            var app = builder.Build();

            // Configure the HTTP request pipeline.
            if (!app.Environment.IsDevelopment())
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseRouting();

            app.UseAuthorization();
            app.UseAuthentication();

            app.MapStaticAssets();

            app.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}"
                )
                .WithStaticAssets();

            using (var scope = app.Services.CreateScope())
            {
                var services = scope.ServiceProvider;
                SeedRoles(services).Wait();
            }
            app.Run();
        }

        public static void ConfigureServices(
            IServiceCollection services,
            IConfiguration configuration
        )
        {
            services.AddDbContext<PlatformDbContext>(options =>
                options.UseSqlite(configuration.GetConnectionString("DefaultConnection"))
            );

            services
                .AddIdentity<User, IdentityRole>()
                .AddEntityFrameworkStores<PlatformDbContext>()
                .AddDefaultTokenProviders();

            services
                .AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
                .AddCookie(options =>
                {
                    options.LoginPath = "/Account/Login";
                    options.AccessDeniedPath = "/Account/AccessDenied";
                });

            services.AddScoped<IEmailService, SMTPEmailService>();

            services.AddAuthorization(options =>
            {
                options.AddPolicy("Admin", policy => policy.RequireRole("Admin"));
            });
        }

        private static async Task SeedRoles(IServiceProvider serviceProvider)
        {
            var roleManager = serviceProvider.GetRequiredService<RoleManager<IdentityRole>>();

            var roles = new[] { "Admin", "User" };

            foreach (var role in roles)
            {
                if (!await roleManager.RoleExistsAsync(role))
                {
                    await roleManager.CreateAsync(new IdentityRole(role));
                }
            }
        }
    }
}