private ClientUser RegisterNewUser(string userName, string password)
{
if (_storageHandler.UserNameExists(userName))
{
throw new UserAlreadyExistException(
$"Account with user name '{userName}' already exists. Please enter another user name and try again.");
}
int userId = _storageHandler.GetNextUserId();
ClientUser newUser = new ClientUser(userId, userName);
_registeredUsers.Add(newUser);
_storageHandler.AddToRegisteredUsers(newUser, password);
return(newUser);
}