Symfony - Implement custom post validator

http://www.symfony-project.org/cookbook/1_2/en/conditional-validator

class YourForm extends sfForm {
  public configure() {
  //...
  // add a post validator
  $this->validatorSchema->setPostValidator(
    new sfValidatorCallback(array('callback' => array($this, 'checkPassword')))
  );
  }

  public function checkPassword($validator, $values)
  {
    if (!empty($values['username']) && $values['password'] != $values['username'])
    {
      $error = new sfValidatorError($validator, 'Invalid password');
 
      // throw an error bound to the password field
      throw new sfValidatorErrorSchema($validator, array('password' => $error));
    }
 
    return $values;
  }
}