如何保证Cookie自动登录的安全？

[php]代码库

$mb = new member();
$mb->db=$this->db;
            
if($mb->checkcookie())
{
    $auth = Zend_Auth::getInstance();
    $authAdapter = new Zend_Auth_Adapter_DbTable($this->db);
    $authAdapter->setTableName('users')
            ->setIdentityColumn('username')
            ->setCredentialColumn('password');
    $authAdapter->setIdentity($mb->user)->setCredential($mb->srpwd);
    $result = $auth->authenticate($authAdapter);
    if ($result->isValid()) {    
        $data = $authAdapter->getResultRowObject(null,'password');
        $auth->getStorage()->write($data);
    }
}