Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Mangary.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Mangary.DAL;

namespace Mangary
{
	public class Startup
	{
		public IConfiguration Configuration { get; }

		public Startup(IConfiguration configuration) => this.Configuration = configuration;

		public void ConfigureServices(IServiceCollection services)
		{
			services.AddDbContext<AppDbContext>(options =>
				options.UseNpgsql(System.Environment.GetEnvironmentVariable("MangaryConnectionString")));

			services.AddIdentity<IdentityUser, IdentityRole>(options => {
				options.User.RequireUniqueEmail = true;
			})
				.AddEntityFrameworkStores<AppDbContext>();

			services.AddAuthentication();
			services.AddAuthorization();

			services.AddScoped<IProductRepository, ProductRepository>();
			services.AddScoped<ICartRepository,    CartRepository>();

			services.ConfigureApplicationCookie(options => {
				options.LoginPath = "/Account/SignIn";
				//options.AccessDeniedPath = "/404";
			});

			services.AddControllersWithViews();
		}

		public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
		{
			if (env.IsDevelopment())
			{
				app.UseDeveloperExceptionPage();
			}
			else
			{
				app.UseExceptionHandler("/Home/Error");
				app.UseHsts();
			}
			/* 
			app.Use(async (context, next) => {
				await next();
				if(context.Response.StatusCode == 404)
				{
					context.Request.Path = "/";
					await next();
				}
			});
			*/
			app.UseHttpsRedirection();
			app.UseStaticFiles();
			app.UseRouting();

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

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