How to use Windows Active Directory Authentication and Identity Based Claims?

Just hit AD with the username and password instead of authenticating against your DB

// POST: /Account/Login
[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
{
    if (ModelState.IsValid)
    {
        var user = await UserManager.FindByNameAsync(model.UserName);
        if (user != null && AuthenticateAD(model.UserName, model.Password))
        {
            await SignInAsync(user, model.RememberMe);
            return RedirectToLocal(returnUrl);
        }
        else
        {
            ModelState.AddModelError("", "Invalid username or password.");
        }
    }
    return View(model);
}

public bool AuthenticateAD(string username, string password)
{
    using(var context = new PrincipalContext(ContextType.Domain, "MYDOMAIN"))
    {
        return context.ValidateCredentials(username, password);
    }
}