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);
}
}