aspnetcore/samples/CookieSample/Startup.cs

using System.Linq;
using System.Security.Claims;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;

namespace CookieSample
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            // This can be removed after https://github.com/aspnet/IISIntegration/issues/371
            services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                options.DefaultChallengeScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            }).AddCookie();
        }

        public void Configure(IApplicationBuilder app)
        {
            app.UseAuthentication();

            app.Run(async context =>
            {
                if (!context.User.Identities.Any(identity => identity.IsAuthenticated))
                {
                    var user = new ClaimsPrincipal(new ClaimsIdentity(new[] { new Claim(ClaimTypes.Name, "bob") }, CookieAuthenticationDefaults.AuthenticationScheme));
                    await context.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, user);

                    context.Response.ContentType = "text/plain";
                    await context.Response.WriteAsync("Hello First timer");
                    return;
                }

                context.Response.ContentType = "text/plain";
                await context.Response.WriteAsync("Hello old timer");
            });
        }
    }
}