Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton(Configuration);
    services.AddSingleton(_users);
    services.AddTransient<IUserService, UserService>();
    services.AddMvc();

    services.AddAuthentication(options =>
        {
            options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            options.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            options.DefaultChallengeScheme = CookieAuthenticationDefaults.AuthenticationScheme;
        })
        .AddCookie(options =>
        {
            options.LoginPath = "/auth/login";
            options.LogoutPath = "/auth/logout";
        });
}