public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
        {
            CustomerEntities db = new CustomerEntities();

            var r = db.客戶資料.Where(o => o.帳號 == model.帳號 && o.密碼 == model.Password).FirstOrDefault();

            //if (!ModelState.IsValid)
            if (r == null)
            {
                return View(model);
            }

            // 這不會計算為帳戶鎖定的登入失敗
            // 若要啟用密碼失敗來觸發帳戶鎖定,請變更為 shouldLockout: true
            var result = await SignInManager.PasswordSignInAsync(model.帳號, model.Password, model.RememberMe, shouldLockout: false);
            switch (result)
            {
                case SignInStatus.Success:
                    return RedirectToLocal(returnUrl);
                case SignInStatus.LockedOut:
                    return View("Lockout");
                case SignInStatus.RequiresVerification:
                    return RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
                case SignInStatus.Failure:
                default:
                    ModelState.AddModelError("", "登入嘗試失試。");
                    return View(model);
            }
        }
        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            //將使用者輸入的字串轉成Base64String
            //string base64Password = Convert.ToBase64String(Encoding.UTF8.GetBytes(Password));
            //todo到DB抓使用者資料
            //假如抓不到系統使用者資料
            //※為了Demo用這種寫法,實際請換成判斷DB的資料存不存在

            CustomerEntities db = new CustomerEntities();
            using (SHA256CryptoServiceProvider csp = new SHA256CryptoServiceProvider())
            {
                var p = Password;
                Password = BitConverter.ToString(csp.ComputeHash(Encoding.Default.GetBytes(p))).Replace("-", "");
            }

            var r = db.客戶資料.Where(o => o.帳號 == Account && o.密碼 == Password).FirstOrDefault();

            if (r == null)
            {
                yield return new ValidationResult("無此帳號或密碼", new string[] { "Account" });
            }
        }