$fb = new Facebook\Facebook([
'app_id' => '{app-id}', // Replace {app-id} with your app id
'app_secret' => '{app-secret}',
'default_graph_version' => 'v2.2',
]);
$helper = $fb->getRedirectLoginHelper();
$permissions = ['email']; // Optional permissions
$loginUrl = $helper->getLoginUrl('https://example.com/fb-callback.php', $permissions);
echo 'Log in with Facebook!';