Facebook access_token

Question

我正在使用fb:multi-friend-selector向朋友发送邀请。一旦用户提交表单，其重定向到一个页面，我获取所选朋友的ID，以便发布到他们的墙上。我已经请求了offline_access的授权，但是当页面加载时会丢弃Uncaught OAuthException错误。我如何使用access_token？

$app_id = APP_ID;
$canvas_page = CANVAS_PAGE_URL;
$auth_url = "http://www.facebook.com/dialog/oauth?client_id="
    . $app_id . "&redirect_uri=" . urlencode($canvas_page)
    . "&scope=publish_stream,email,offline_access";
$signed_request = $_REQUEST["signed_request"];

list($encoded_sig, $payload) = explode('.', $signed_request, 2);
$data = json_decode(base64_decode(strtr($payload, '-_', '+/')), true);

if (empty($data["user_id"])) {
    echo("<script> top.location.href='" . $auth_url . "'</script>");
} else {
    include 'resources/friendInvitationForm.php';
}


require '../src/facebook.php';

//// Create our Application instance.
$facebook = new Facebook(array(
    'appId' => 'xxxxxxxxxxxxxxxx',
    'secret' => 'xxxxxxxxxxxxxxxxxxx',
    'cookie' => 'true'
));

$friends = (isset($_REQUEST["ids"]) ? $_REQUEST["ids"] : null);
$count = count($friends);
$attachment = array(
    'message' => 'this is my message',
    'name' => 'This is my demo Facebook application!',
    'caption' => "Caption of the Post",
    'link' => 'http://www.facebook.com/pages/Cosmetics/167231286678063'
        . '?sk=app_233227910028874',
    'description' => 'this is a description',
    'picture' => 'http://mysite.com/pic.gif',
    'actions' => array(array(
        'name' => 'Get Search',
        'link' => 'http://www.google.com'))
);

for($i = 0; $i <= $count; $i++)
{
    $result = $facebook->api('/'.$friends[$i].'/feed/','post',$attachment);
}