Store the right signed request after page like - php

Question

I have a little Facebook app, which has a "like gate" at the beginning. The user have to like the page to use the app. The app itself has some subpages, so I have to store the signed request into $_SESSION variable if I want the subpages to work. My problem is that the signed request is only sent on app load and at this time the user hasn't liked the page yet. So if this time the signed request is saved, the $signed_request["page"]["liked"] will alway return FALSE... How can I reload the signed request?
FQL and $like_data = $facebook->api('/me/likes/PAGE-ID/'); isn't good, because I want the permission dialog AFTER the page like.
This is the code right now:
$page_id = $signed_request["page"]["id"];
$like_status = $signed_request["page"]["liked"];
if(!$like_status){
header("Location: notfan.php");
exit;
}else{
if (!isset($_SESSION["SR"]))
{
$_SESSION["SR"] = $_REQUEST["signed_request"];
}else{
$encoded_sig = null;
$payload = null;
list($encoded_sig, $payload) = explode('.', $_SESSION["SR"], 2);
$sig = base64_decode(strtr($encoded_sig, '-_', '+/'));
$signed_request = $data = json_decode(base64_decode(strtr($payload, '-_', '+/'), true));
$signed_request = objectToArray($signed_request);
}
}
Thank you very much!

Answer 1

just save the signed request every time you encounter it in the request: When the user likes the page, Facebook will do a page reload and resends the signed request
edit:
You're setting $like_status and checking it before you even know if you have a signed request and before you set the value of $like_status.
I would check the request parameter first, the session second, then fill the $like_status variable, then check the $like_status.
Something like this:
if( isset($_POST['signed_request']) )
{
$_SESSION["SR"] = $_REQUEST["signed_request"];
}
if (!isset($_SESSION["SR"]))
{
//shouldn't even happen now when page is opened through facebook,
//so you might want some error handling here
}
$encoded_sig = null;
$payload = null;
list($encoded_sig, $payload) = explode('.', $_SESSION["SR"], 2);
$sig = base64_decode(strtr($encoded_sig, '-_', '+/'));
$signed_request = $data = json_decode(base64_decode(strtr($payload, '-_', '+/'), true));
$signed_request = objectToArray($signed_request);
$page_id = $signed_request["page"]["id"];
$like_status = $signed_request["page"]["liked"];
if(!$like_status){
header("Location: notfan.php");
exit;
}