public async Task<ActionResult> Register(RegisterViewModel model)
        {
            if (ModelState.IsValid)
            {
                var user = new CustomUser()
                {
                    UserName = model.UserName,
                    FirstName = model.FirstName,
                    LastName = model.LastName
                };
                var result = await UserManager.CreateAsync(user, model.Password);
                if (result.Succeeded)
                {
                    await SignInAsync(user, isPersistent: false);
                    return RedirectToAction("Index", "Home");
                }
                else
                {
                    AddErrors(result);
                }
            }

            // If we got this far, something failed, redisplay form
            return View(model);
        }
        private async Task SignInAsync(CustomUser user, bool isPersistent)
        {
            AuthenticationManager.SignOut(DefaultAuthenticationTypes.ExternalCookie);
            var identity = await UserManager.CreateIdentityAsync(user, DefaultAuthenticationTypes.ApplicationCookie);

            await SetExternalProperties(identity);

            AuthenticationManager.SignIn(new AuthenticationProperties() { IsPersistent = isPersistent }, identity);

            await SaveAccessToken(user, identity);

        }
        private async Task SaveAccessToken(CustomUser user, ClaimsIdentity identity)
        {
            var userclaims = await UserManager.GetClaimsAsync(user.Id);

            foreach ( var at in (
                from claims in identity.Claims
                where claims.Type.EndsWith("access_token")
                select new Claim(claims.Type, claims.Value, claims.ValueType, claims.Issuer)))
                {

                    if (!userclaims.Contains(at))
                    {
                        await UserManager.AddClaimAsync(user.Id, at);
                    }

                };
        }
        public async Task<ActionResult> ExternalLoginConfirmation(ExternalLoginConfirmationViewModel model, string returnUrl)
        {
            if (User.Identity.IsAuthenticated)
            {
                return RedirectToAction("Manage");
            }

            if (ModelState.IsValid)
            {
                // Get the information about the user from the external login provider
                var info = await AuthenticationManager.GetExternalLoginInfoAsync();
                if (info == null)
                {
                    return View("ExternalLoginFailure");
                }
                var user = new CustomUser() { UserName = model.UserName };
                var result = await UserManager.CreateAsync(user);
                if (result.Succeeded)
                {
                    result = await UserManager.AddLoginAsync(user.Id, info.Login);
                    if (result.Succeeded)
                    {
                        await SignInAsync(user, isPersistent: false);
                        return RedirectToLocal(returnUrl);
                    }
                }
                AddErrors(result);
            }

            ViewBag.ReturnUrl = returnUrl;
            return View(model);
        }