如何使用facebook php sdk v5从facebook登录注销？

Question

I integrate my site login from facebook login and i have successfully login from facebook login. i have used facebook php sdk v5.

i want to logout programmatically when i click logout button and i have faces another issue if i opened my login link after 6hrs it is automatically login.

i want to expire session. please review my code if i have done wrong code for login please check out.

my code:

session_start();
require_once __DIR__ . '/src/Facebook/autoload.php';
$fb = new Facebook\Facebook([
  'app_id' => 'app_id',
  'app_secret' => 'app_secret',
  'default_graph_version' => 'v2.5',
  ]);
$helper = $fb->getRedirectLoginHelper();
$permissions = ['email']; 
try {
    if (isset($_SESSION['facebook_access_token'])) {
        $accessToken = $_SESSION['facebook_access_token'];
    } else {
        $accessToken = $helper->getAccessToken();
    }
} catch(Facebook\Exceptions\FacebookResponseException $e) {
    // When Graph returns an error
    echo 'Graph returned an error: ' . $e->getMessage();
    exit;
} catch(Facebook\Exceptions\FacebookSDKException $e) {
    // When validation fails or other local issues
    echo 'Facebook SDK returned an error: ' . $e->getMessage();
    exit;
 }
if (isset($accessToken)) {
    if (isset($_SESSION['facebook_access_token'])) {
        $fb->setDefaultAccessToken($_SESSION['facebook_access_token']);
    } else {
        // getting short-lived access token
        $_SESSION['facebook_access_token'] = (string) $accessToken;
        // OAuth 2.0 client handler
        $oAuth2Client = $fb->getOAuth2Client();
        // Exchanges a short-lived access token for a long-lived one
        $longLivedAccessToken = $oAuth2Client->getLongLivedAccessToken($_SESSION['facebook_access_token']);
        $_SESSION['facebook_access_token'] = (string) $longLivedAccessToken;
        // setting default access token to be used in script
        $fb->setDefaultAccessToken($_SESSION['facebook_access_token']);
    }
    // redirect the user back to the same page if it has "code" GET variable
    if (isset($_GET['code'])) {
        header('Location: ./');
    }
    // getting basic info about user
    try {
        $profile_request = $fb->get('/me?fields=about,bio,birthday,email,gender,first_name,last_name,name,timezone,picture.width(200)');
        $profile = $profile_request->getGraphNode()->asArray();
    } catch(Facebook\Exceptions\FacebookResponseException $e) {
        // When Graph returns an error
        echo 'Graph returned an error: ' . $e->getMessage();
        session_destroy();
        // redirecting user back to app login page
        header("Location: ./");
        exit;
    } catch(Facebook\Exceptions\FacebookSDKException $e) {
        // When validation fails or other local issues
        echo 'Facebook SDK returned an error: ' . $e->getMessage();
        exit;
    }

    // printing $profile array on the screen which holds the basic info about user
    //print_r($profile);
    echo "<br> Logged in as ".$profile['email'];
    echo $_SESSION['facebook_access_token'];
    // Now you can redirect to another page and use the access token from $_SESSION['facebook_access_token']
} else {
    // replace your website URL same as added in the developers.facebook.com/apps e.g. if you used http instead of https and you used non-www version or www version of your website then you must add the same here
    $loginUrl = $helper->getLoginUrl('http://www.example.com/fbapp/index.php', $permissions);
    echo "<script>window.top.location.href='".$loginUrl."'</script>";

    //echo '<a href="' . $loginUrl . '">Log in with Facebook!</a>';
}
$logoutUrl = 'https://www.facebook.com/logout.php?next=http://www.example.com/fbapp/index.php&access_token=' . $_SESSION['facebook_access_token'];
    echo "<a href='" . $logoutUrl . "'>Logout with Facebook!</a>";