Facebook page tab app session across subpages PHP SDK 4 - facebook

Question

See the full original question further down
Using the latest Facebook PHP SDK 4.4.0, in my main app page I can do the following to get a user id etc.
<?php
FacebookSession::setDefaultApplication(APP_ID, SECRET);
$helper = new FacebookRedirectLoginHelper( PAGE_URL );
$pageHelper = new FacebookPageTabHelper();
$session = $pageHelper->getSession();
echo '<p>You are currently viewing page: '. $pageHelper->getPageId() . '</p>';
// get user_id
echo '<p>User Id: ' . $pageHelper->getUserId() . '</p>';
// **depcrecated** get like status - use for likegates
echo '<p>You have '. ( $pageHelper->isLiked() ? 'LIKED' : 'NOT liked' ) . ' this page</p>';
// get admin status
echo '<p>You are '. ( $pageHelper->isAdmin() ? 'an ADMIN' : 'NOT an ADMIN' ) . '</p>';
?>
This does not work on sub pages of my app ... Why is the session (and amongst other things, the signed request) lost? How can I get them back and how can I get methods such as getUserId() from the the FacebookPageTabHelper to continue to work on sub pages?
full original question
I'm fairly new to Facebook app development and I'm having problems with session management and I just can't seem to be able to wrap my head around it. Of course it doesn't help that the official documentation is almost useless.
My problem is that the page session get lost when moving away from the apps main page to a subpage within the Facebook page tab app iframe.
I use the following PHP code to obtain the session and user id on the main (initial) app page and it works great:
<?php
FacebookSession::setDefaultApplication(APP_ID, SECRET);
$helper = new FacebookRedirectLoginHelper( PAGE_URL );
$pageHelper = new FacebookPageTabHelper();
$session = $pageHelper->getSession();
?>
But it doesn't work on sub pages :( when a user clicks on a menu item (or any other link inside the app/iframe), the session goes bye bye. Which is not ideal as I need the user id of the user to track whether or not that user has completed certain actions. Of course I could send the ID along with every request, but there must be a way to have a persisting session, no?
Is there a way to retrieve the session on a sub page in PHP? If so, how? Or do I have to load additional content using javascript? And how would that work, if I can't keep the session between requests and therefore have no way of identifying which user a request came from? How do others handle this?
What I'd like to avoid is to write my own user session management, which would solve the problem but is simply not in the budget and I was hoping I could work with what Facebook already had on offer. Especially since my app doesn't require user information/permissions of any kind.
Thanks a lot in advance for any info on this topic, greatly appreciated, going in circles here.
Edit to clarify: I thought of just saving the Facebook session in a PHP session cookie, but how would I use that to reconnect with Facebook after changing the page?

Answer 1

I finally managed to solve this problem. I'm not sure whether this is considered the right way or can even be a recommended way of doing this, but it works and since time is of the essence, I don't have much of a choice.
If anybody has any further ideas or suggestions, please comment.
Here's how I did it:
// store the signed request
if(isset($_REQUEST['signed_request'])) {
$_SESSION['signed_request'] = $_REQUEST['signed_request'];
} elseif($_SESSION['signed_request']) {
$_REQUEST['signed_request'] = $_GET['signed_request'] = $_POST['signed_request'] = $_SESSION['signed_request'];
}
// assign the stored signed request to REQUEST, GET and POST vars (the unsavory bit, imo)
$_REQUEST['signed_request'] = $_GET['signed_request'] = $_POST['signed_request'] = $_SESSION['signedRequest'];
FacebookSession::setDefaultApplication(APP_ID, APP_SECRET);
$accessToken = APP_ID . '|' . APP_SECRET;
$this->session = new FacebookSession($accessToken);
$pageHelper = new FacebookPageTabHelper();
$isAdmin = ($this->pageHelper->getPageData('admin')) ? $this->pageHelper->getPageData('admin') : 0;
// get pade id
echo '<p>You are currently viewing page: '. $pageHelper->getPageId() . '</p>';
// get user_id
echo '<p>User Id: ' . $pageHelper->getUserId() . '</p>';
// get admin status
echo '<p>You are '. ( $isAdmin ? 'an ADMIN' : 'NOT an ADMIN' ) . '</p>';