public User CreateUser(string identifier, string password, string name, UserType userType = UserType.Cashier)
        {
            if (string.IsNullOrEmpty(identifier) || string.IsNullOrEmpty(password))
            {
                throw new ArgumentNullException();
            }

            var user = new User()
            {
                Identifier = identifier,
                Password = password,
                UserType = userType
            };

            throw new NotImplementedException();
        }
 public User UnlockUser(User user)
 {
     throw new NotImplementedException();
 }
 public User RemoveUser(User user)
 {
     throw new NotImplementedException();
 }
 public User ChangePassword(User user, string password)
 {
     throw new NotImplementedException();
 }