fb-callback.php

<?php
session_start();
include_once("config.php");
if (isset($_GET['state'])) {
    $helper->getPersistentDataHandler()->set('state', $_GET['state']);
}
try {
  $accessToken = $helper->getAccessToken();
} catch(Facebook\Exceptions\FacebookResponseException $e) {
  echo 'Graph returned an error: ' . $e->getMessage();
  exit;
} catch(Facebook\Exceptions\FacebookSDKException $e) {
  echo 'Facebook SDK returned an error: ' . $e->getMessage();
  exit;
}

if (! isset($accessToken)) {
  if ($helper->getError()) {
    header('HTTP/1.0 401 Unauthorized');
    echo "Error: " . $helper->getError() . "\n";
    echo "Error Code: " . $helper->getErrorCode() . "\n";
    echo "Error Reason: " . $helper->getErrorReason() . "\n";
    echo "Error Description: " . $helper->getErrorDescription() . "\n";
  } else {
    header('HTTP/1.0 400 Bad Request');
    echo 'Bad request';
  }
  exit;
}
$oAuth2Client = $fb->getOAuth2Client();
$tokenMetadata = $oAuth2Client->debugToken($accessToken);
$tokenMetadata->validateAppId($appId);
$tokenMetadata->validateExpiration();
if (! $accessToken->isLongLived()) {
  try {
    $accessToken = $oAuth2Client->getLongLivedAccessToken($accessToken);
  } catch (Facebook\Exceptions\FacebookSDKException $e) {
    echo "<p>Error getting long-lived access token: " . $helper->getMessage() . "</p>\n\n";
    exit;
  }
}
$_SESSION['fb_access_token'] = (string) $accessToken;
header('Location: index.php');
?>