Startup_Configure.cs

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddSerilog();
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
                app.UseHttpsRedirection();
            }

            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseSession(); // <-----
            
            app.UseMvc();
        }