public ActionResult Signin(string returnUrl)
        {
            SignInModel model = new SignInModel();
            model.ReturnUrl = returnUrl;

            return View(model);
        }
        public ActionResult Signin(SignInModel model)
        {
            if (ModelState.IsValid == false)
                return View(model);

            Person signinPerson; 
            using (CrdbContext ctx = new CrdbContext())
            {
                signinPerson = PersonBL.ValidateAndLoad(model.Email, model.Password, ctx); 
            }
            if (signinPerson == null)
            {
                ModelState.AddModelError("", "Giriş yapılamadı. Lütfen bilgilerinizi kontrol edip tekrar deneyiniz.  ");
                return View(model);
            }
            AppUser appUser = AppUser.FromPerson(signinPerson);
            IdentitySignin(appUser, null, model.RememberMe);

            if (string.IsNullOrEmpty(model.ReturnUrl))
                model.ReturnUrl = Url.Action("Index", "Home");

            return Redirect(model.ReturnUrl);
        }