private async Task SignInAsync(User user, bool isPersistent)
{
AuthenticationManager.SignOut(DefaultAuthenticationTypes.ExternalCookie);
var identity = await UserManager.CreateIdentityAsync(user, DefaultAuthenticationTypes.ApplicationCookie);
identity.AddClaim(new Claim("ImageUrl", user.GetImageUrl()));
AuthenticationManager.SignIn(new AuthenticationProperties() { IsPersistent = isPersistent }, identity);
}