fb-callback.php

<?php
		require_once "config.php";

		if (!isset($_SESSION['email']) && empty($_SESSION['email'])) {
			// code...
			try {
				$accessToken = $helper->getAccessToken();
			} catch (\Facebook\Exceptions\FacebookResponseException $e) {
				echo "Response Exception: " . $e->getMessage();
				exit();
			} catch (\Facebook\Exceptions\FacebookSDKException $e) {
				echo "SDK Exception: " . $e->getMessage();
				exit();
			}

			if (!$accessToken) {
				header('Location: login.php');
				exit();
			}

			$oAuth2Client = $FB->getOAuth2Client();
			if (!$accessToken->isLongLived())
				$accessToken = $oAuth2Client->getLongLivedAccessToken($accessToken);

			$response = $FB->get("/me?fields=id, first_name, last_name, email, picture.type(large)", $accessToken);
			$userData = $response->getGraphNode()->asArray();
			var_dump($userData);
			$_SESSION['userData'] = $userData;
			$_SESSION['access_token'] = (string)$accessToken;
		}
  header('location: ./login.php');
	exit();
?>