/**
  * Gets the password from the model and matches it against the value supplied
  * @param string $value The password to match
  * @return boolean Returns true if the passwords match, false otherwise
  */
 public function isValid($value)
 {
     $this->_setValue($value);
     $value = md5($this->_model->getUsername() . $value);
     if (!($this->_model->getPassword() == $value)) {
         $this->_error();
         return false;
     }
     return true;
 }