First of all, you don't have to edit PHP SDK, below is the sample for authenticating the user and then redirecting to your landing page,
Make sure you replace:
YOUR-APP-ID-HERE with Your facebook application id,
YOUR-APP-API-SECRET-HERE with Your facebook application secret key
YOUR-REDIRECT-URL-HERE with Your landing page URL
<?php
// Requires Facebook PHP SDK 3.0.1: https://github.com/facebook/php-sdk/
require ('facebook.php');
define('FACEBOOK_APP_ID',"YOUR-APP-ID-HERE");
define('FACEBOOK_SECRET',"YOUR-APP-API-SECRET-HERE");
define('REDIRECT_URI',"YOUR-REDIRECT-URL-HERE");
$user = null;
$facebook = new Facebook(array(
'appId' => FACEBOOK_APP_ID,
'secret' => FACEBOOK_SECRET,
'cookie' => true
));
$user = $facebook->getUser(); // Get the UID of the connected user, or 0 if the Facebook user is not connected.
if($user == 0) {
// If the user is not connected to your application, redirect the user to authentication page
/**
* Get a Login URL for use with redirects. By default, full page redirect is
* assumed. If you are using the generated URL with a window.open() call in
* JavaScript, you can pass in display=popup as part of the $params.
*
* The parameters:
* - redirect_uri: the url to go to after a successful login
* - scope: comma separated list of requested extended perms
*/
$login_url = $facebook->getLoginUrl($params = array('redirect_uri' => REDIRECT_URI));
echo ("<script> top.location.href='".$login_url."'</script>");
} else {
// if the user is already connected, then redirect them to landing page or show some content
echo ("<script> window.location.href='".REDIRECT_URI."'</script>");
}
?>
If you want to get extended permissions, then simply add another "scope" parameter to the login url, ex:
$login_url = $facebook->getLoginUrl($params = array('redirect_uri' => REDIRECT_URI,'scope' => 'comma-separated-list-of-requested-extended-perms'));
For more details on permissions, refer facebook permissions docs