PrincipalContext ValidateCredentials async

Question

I would like to have the PrincipalContext ValidateCredentials method made async.

     public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
    {

    using (PrincipalContext pc = new PrincipalContext(ContextType.Domain, "gob.uk"))
        {

            if (pc.ValidateCredentials(model.Email, model.Password))
            {
                returnUrl = "/Home/index";
                return RedirectToLocal(returnUrl);
            }
            else
            {
                ModelState.AddModelError("", "Invalid login attempt.");
                return View(model);
            }
        }
  }

As you can see I am trying to use Active Directory to authenticate users, but it seems that pc.ValidateCreadentials is a sync method. How can I make it async?