Form Validation Callback for Matching Password

[eluser]RMinor[/eluser]
I am trying to validate a form that administrators will use to change their passwords. I am salting and using sha1() on the password when I store it in the database. When an administrator is changing their password I am checking that the password they enter as their old one is actually correct. For this I need to pass in their id and the entered password value. How do I do this using the form validation callback feature and multiple input parameters to it?

Controller

Code:

/**
  * Default method for this controller
  */
public function index()
{
  // Retrieve page information
  $data['page_info'] = $this->Global_model->pageInfo($this->_page);
  // Retrieve the administrator's id value from teh session
  $admin_id = $this->session->userdata('admin_id');
  // Load the form helper
  $this->load->helper('form');
  // Check if the submit button was pressed
  if ($this->input->post('submit')) {
   // Load the form validation library
   $this->load->library('form_validation');
   // Set form validation rules
   $this->form_validation->set_rules('old_password', 'Old Password', 'trim|required|callback_password_matches');
   $this->form_validation->set_rules('new_password', 'New Password', 'trim|required');
   $this->form_validation->set_rules('confirm_password', 'Confirm Password', 'trim|required|matches[new_password]');
   // Run form validation
   if($this->form_validation->run() == FALSE) {} else {
    // Retrieve the administrator's email address
    $email = $this->Administrator_model->getEmail($admin_id);
    // Assign input to variables
    $old_password = $this->input->post('old_password');
    $new_password = $this->input->post('new_password');
    // Attempt to change password
    if ($this->Administrator_model->changePassword($email, $old_password, $new_password)) {
     $data['success'] = TRUE;
    } else {
     $data['success'] = FALSE;
    }
   }
  }
  $this->load->view('employer/change-password_view', $data);
}

/**
  * Method to perform a password match during form validation
  * @param string $email
  * @param string $passowrd
  * @return boolean
  */
public function password_matches($id, $passowrd)
{
  if (!$this->User_model->passwordMatches($id, $password)) {
   $this->form_validation->set_message('password_matches', 'The password you entered does not match your old password.');
   return FALSE;
  } else {
   return TRUE;
  }
  
}

Model

Code:

/**
  * Method to determine if a password matches what is stored in the database
  * @param integer $id
  * @param string $password
  * @return boolean
  */
public function passwordMatches($id, $password)
{
  $query = $this->db->query("SELECT admin_salt
   FROM admin
   WHERE admin_id = ?", array($id));
  if ($query->num_rows() == 1) {
   $result = $query->row_array();
   $salt = $result['admin_salt'];
  }
  $hashed_password = sha1($salt . $password);
  $query = $this->db->query("SELECT admin_id
   FROM admin
   WHERE admin_id = ?
   AND admin_password = ?", array(
    $id,
    $hashed_password
   ));
  if ($query->num_rows() == 1) {
   return TRUE;
  }
  return FALSE;
}