Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using api.Services;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using MongoDB.Driver;

namespace api
{
    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)
        {
            services.AddSingleton<MongoService>(new MongoService() { 
                Client = new MongoClient(String.Format("mongodb://{0}:{1}", Configuration["URI"], Configuration["PORT"] )) 
            });
            services.AddScoped<TodoService>();

            services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                options.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            }).AddCookie(options=>{
                options.Cookie.SecurePolicy = CookieSecurePolicy.SameAsRequest;
                options.Cookie.SameSite = SameSiteMode.None;
            }) ;

            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            app.UseCors(builder =>
            {
                builder.WithOrigins(
                    "http://localhost:4200"
                ).AllowCredentials().AllowAnyMethod().AllowAnyHeader();
            });
            
            if (env.IsDevelopment()) app.UseDeveloperExceptionPage();
            else app.UseHsts();

            app.UseAuthentication();
            app.UseHttpsRedirection();

            app.UseMvc(routers =>
            {
                // routers.MapRoute(
                //     name: "default",
                //     template: "{controller}/{action}",
                //     defaults: new { controller = "Welcome", action = "Index" }
                // );
            });
        }
    }
}