Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using angular_observables_api.Models;

namespace angular_observables_api
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<TodoContext>(opt => 
                opt.UseInMemoryDatabase("TodoList"));
            services.AddCors();
            services.AddMvc()
                    .SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

        public void Configure(IApplicationBuilder app)
        {
            app.UseCors(builder =>
                builder
                    .WithOrigins("http://localhost:4200")
                    .AllowAnyHeader()
                    .AllowAnyMethod());
            app.UseMvc();
        }
    }
}