public function authenticate()
{
$users = array('demo' => 'demo', 'admin' => 'admin');
if (!isset($users[$this->username])) {
$this->errorCode = self::ERROR_USERNAME_INVALID;
} elseif ($users[$this->username] !== $this->password) {
$this->errorCode = self::ERROR_PASSWORD_INVALID;
} else {
$this->errorCode = self::ERROR_NONE;
}
return !$this->errorCode;
}