unity + php get Authentication

Hellow. My problem is this:

I try to make post on facebook a photo that a have in my unity 3d Applications. Simply I do some like this:

(...)

WWW upload = new WWW("http://.../face/upload.php",postForm);
yield return upload;

in "php" file i simply get user information... and if i run it on a Browser, it works perfectly... so to unity it dosn't get the Authentication....

Any sugestion???