public Task AddLoginAsync(TUser user, UserLoginInfo login)
        {
            if (user == null)
            {
                throw new ArgumentNullException("user");
            }
            if (login == null)
            {
                throw new ArgumentNullException("login");
            }
            CustomUserLogin l = new CustomUserLogin {
                LoginProvider = login.LoginProvider, ProviderKey = login.ProviderKey, UserId = user.Id
            };

            user.Logins.Add(l);
            saveFileUsers();
            return(Task.FromResult(0));
        }
        public Task RemoveLoginAsync(TUser user, UserLoginInfo login)
        {
            if (user == null)
            {
                throw new ArgumentNullException("user");
            }
            if (login == null)
            {
                throw new ArgumentNullException("login");
            }
            CustomUserLogin l = user.Logins.FirstOrDefault(x => x.LoginProvider == login.LoginProvider && x.ProviderKey == login.ProviderKey);

            if (l != null)
            {
                user.Logins.Remove(l);
                saveFileUsers();
            }
            return(Task.FromResult(0));
        }