Kohana 3.3 check old password is correct before changing password

Using Auth ORM, how can I tell if the old password is correct before changing the password. I have seen code for older versions of Kohana which uses the find_salt method, but this no longer applicable in version 3.3.

Any ideas?

There is a better way to do this using Validation class:

if($post = $this->request->post()) {
    $user = Auth::instance()->get_user();

    $validation = Validation::factory($post)
        ->rule('old_password', array(Auth::instance(), 'check_password'));

    // Rules for password (model rules applies after hash)
    $extra_rules = Validation::factory($post)
        ->rule('password', 'not_empty')
        ->rule('password', 'min_length', array(':value', 8))
        ->rule('password', 'matches', array(':validation', 'password', 'password_confirm'));

    try {
        if(!$validation->check()) {
            throw new ORM_Validation_Exception('password', $validation);
        }
        $user->password = $post['password'];
        $user->update($extra_rules);
    }catch(ORM_Validation_Exception $e){
        // Handle errors
    }
}