Facebook API: How to post to own application wall without login

I want to post to my own application wall a text with a script but without to login first because it should be done automatically. How could I do that? I tried already:

$fb = new Facebook(array(
    'appId'  => 'appid',
    'secret' => 'appsecret',
    'cookie' => true
));


if ($fb->getSession()) {
    // Post
} else {
    // Logger
    // Every time I get in here :(
}

What do I have to do to get the access to post to my the own app wall with a script?