How to let a user choose different Facebook permissions in the same page? - facebook-php-sdk

Question

Suppose you want to build a webpage with Facebook PHP SDK, where you want to allow the user to select the information Facebook will return to the server. I've came with the following code to allow an user to either choose from allowing Facebook to send only the basic profile or else to also send the pages managed by this user.
session_start();
// Load the Facebook PHP SDK
require_once __DIR__ . '/facebook-sdk-v5/autoload.php';
define('APP_ID', 'xxxxxxxxxxx');
define('APP_SECRET', 'xxxxxxxxxxxxxxxxxxxx');
$fbProfile = new Facebook\Facebook([
'app_id' => APP_ID,
'app_secret' => APP_SECRET,
'default_graph_version' => 'v2.7'
]);
$fbPages = new Facebook\Facebook([
'app_id' => APP_ID,
'app_secret' => APP_SECRET,
'default_graph_version' => 'v2.7'
]);
$helperProfile = $fbProfile->getRedirectLoginHelper();
$redirectUrlProfile = 'http://www.example.com/link1.php';
$loginUrlProfile = $helperProfile->getLoginUrl($redirectUrlProfile);
echo 'Get profile with Facebook!<br>';
$helperPages = $fbPages->getRedirectLoginHelper();
$permissions = ['pages_show_list']; // Optional permissions
$redirectUrlPages = "http://www.example.com/link2.php";
$loginUrlPages = $helperPages->getLoginUrl($redirectUrlPages, $permissions);
echo 'Get pages with Facebook!';
If I use the above code (commenting the non-relevant parts) with only one facebook object to either retrieve the profile or the pages managed by user (but not both), everything works fine. But if I use both objects concurrently to give a choice to the user, I get a FacebookSDKException. I guess this is due to CRSF cookies.
Is there any way to circunvent this problem?

Answer 1

I guess this is due to CRSF cookies.
Correct. Calling the getLoginUrl method creates a new random state value and writes it into the session, overwriting any previously stored one.
So if you call the method twice (or more times), login will only work if you call the login dialog via the last login URL created, because only that contains a state value that matches the one stored in the session.
If you want to keep using two different redirect URIs, then you need to implement an additional step to create the correct login URL, and only that one.
So you have two links in your page, both pointing to a script on your server, and passing what permissions to ask for via a GET parameter (whether you want to pass permission names directly, or just a flag like ?loginmode=1/?loginmode=2, is up to you.)
In that script, you decide which redirect URI and scope value to call the getLoginUrl method with - once. And then your script just redirects to that login URL.
(But keep in mind that the step that exchanges the code for an access token also requires the redirect URI parameter to be passed, again - and again with the exact same value that was used in the login dialog call.)
So doing it the way #luschn suggested in comments, using the JS SDK for login purposes, is probably much easier. FB.login can be called with different scopes from different points in your client-side JS code without any such problems.