Startup.cs

using System;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using WebClient.Filters;
using WebClient.Services;

namespace WebClient
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            System.Net.ServicePointManager.ServerCertificateValidationCallback +=
                (sender, certificate, chain, sslPolicyErrors) => true;

            services.AddDistributedMemoryCache();
            services.AddSession(options =>
            {
                options.IdleTimeout = TimeSpan.FromSeconds(300);
                options.Cookie.HttpOnly = true;
                options.Cookie.IsEssential = true;
            });

            services.AddControllersWithViews(options =>
            {
                options.Filters.Add(new LoginFilter());
            });
            ConfigureAppServices(services);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseSession();

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

        // Configuration of singletons from services folder used by controllers
        private void ConfigureAppServices(IServiceCollection services)
        {
            services.AddSingleton<LoginService>();
            services.AddSingleton<PostsService>();
            services.AddSingleton<StatisticsService>();
            services.AddSingleton<UsersService>();
        }
    }
}