Minimal Identity Authenticator

AccountController.cs

public class AccountController : Controller
{
    private readonly Authenticator authenticator = new Authenticator();

    public ActionResult Login()
    {
        return View();
    }

    [HttpPost, ValidateAntiForgeryToken]
    public ActionResult Login(LoginViewModel model)
    {
        if (ModelState.IsValid)
        {
            var authenticated = authenticator.Login(model.Username, model.Password);
            if (authenticated)
            {
                return RedirectToAction("Index", "Home");
            }

            ModelState.AddModelError("", "Invalid username or password.");
        }
        return View(model);
    }

    public ActionResult Register()
    {
        return View();
    }

    [HttpPost, ValidateAntiForgeryToken]
    public ActionResult Register(RegisterViewModel model)
    {
        if (ModelState.IsValid)
        {
            var result = authenticator.Register(model.Username, model.Password);

            if (result.Succeeded)
            {
                return RedirectToAction("Index", "Home");
            }

            foreach (var error in result.Errors)
            {
                ModelState.AddModelError("", error);
            }
        }
        return View(model);
    }

    public ActionResult SignOut()
    {
        authenticator.SignOut();
        return RedirectToAction("Index", "Home");
    }
}

Authenticator.cs

public class Authenticator
{
    private UserManager<IdentityUser> UserManager
    {
        get
        {
            var store = new UserStore<IdentityUser>();
            return new UserManager<IdentityUser>(store);
        }
    }

    private IAuthenticationManager AuthenticationManager
    {
        get { return HttpContext.Current.GetOwinContext().Authentication; }
    }

    public IdentityResult Register(string username, string password)
    {
        var user = new IdentityUser { UserName = username };
        var result = UserManager.Create(user, password);

        if (result.Succeeded)
        {
            Authenticate(user, false);
        }

        return result;
    }

    public bool Login(string username, string password, bool persistant = false)
    {
        var user = UserManager.Find(username, password);

        if (user != null)
        {
            Authenticate(user, persistant);
            return true;
        }

        return false;
    }

    public void Authenticate(IdentityUser user, bool persistent)
    {
        var identity = UserManager.CreateIdentity(user, DefaultAuthenticationTypes.ApplicationCookie);
        var authenticationProperties = new AuthenticationProperties { IsPersistent = persistent };
        AuthenticationManager.SignIn(authenticationProperties, identity);
    }

    public void SignOut()
    {
        AuthenticationManager.SignOut();
    }
}

LoginViewModel.cs

public class LoginViewModel
{
    [Required]
    public string Username { get; set; }

    [Required]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [Display(Name = "Remember me?")]
    public bool RememberMe { get; set; }
}

packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="bootstrap" version="3.0.0" targetFramework="net45" />
  <package id="EntityFramework" version="6.1.1" targetFramework="net45" />
  <package id="jQuery" version="1.10.2" targetFramework="net45" />
  <package id="Microsoft.AspNet.Identity.Core" version="2.0.1" targetFramework="net45" />
  <package id="Microsoft.AspNet.Identity.EntityFramework" version="2.0.1" targetFramework="net45" />
  <package id="Microsoft.AspNet.Identity.Owin" version="2.0.1" targetFramework="net45" />
  <package id="Microsoft.AspNet.Mvc" version="5.1.2" targetFramework="net45" />
  <package id="Microsoft.AspNet.Razor" version="3.1.2" targetFramework="net45" />
  <package id="Microsoft.AspNet.WebPages" version="3.1.2" targetFramework="net45" />
  <package id="Microsoft.Owin" version="2.1.0" targetFramework="net45" />
  <package id="Microsoft.Owin.Host.SystemWeb" version="2.1.0" targetFramework="net45" />
  <package id="Microsoft.Owin.Security" version="2.1.0" targetFramework="net45" />
  <package id="Microsoft.Owin.Security.Cookies" version="2.1.0" targetFramework="net45" />
  <package id="Microsoft.Owin.Security.OAuth" version="2.1.0" targetFramework="net45" />
  <package id="Microsoft.Web.Infrastructure" version="1.0.0.0" targetFramework="net45" />
  <package id="Modernizr" version="2.6.2" targetFramework="net45" />
  <package id="Newtonsoft.Json" version="4.5.11" targetFramework="net45" />
  <package id="Owin" version="1.0" targetFramework="net45" />
</packages>

RegisterViewModel.cs

public class RegisterViewModel
{
    [Required]
    [Display(Name = "Username")]
    public string Username { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }
}

Startup.cs

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
            LoginPath = new PathString("/Login")
        });
    }
}