Facebook login (dari docs facebook)

facebook_login.php

<?php 
$app_id   = "YOUR-APP-ID";
$app_secret = "YOUR-APP-SECRET-ID";
$my_url 	= "YOUR-CALLBACK-URL";
//$my_url   = "http://yusyaif.com/facebook";
$code 		= $_REQUEST["code"];

session_start();

if(empty($code)) {
	$_SESSION['state'] = md5(uniqid(rand(), TRUE)); // CSRF protection
	$dialog_url = "https://www.facebook.com/dialog/oauth?client_id=" 
					. $app_id . "&redirect_uri=" 
					. urlencode($my_url) . "&state="
					. $_SESSION['state'];

	echo("<script> top.location.href='" . $dialog_url . "'</script>");
}

   if($_SESSION['state'] && ($_SESSION['state'] === $_REQUEST['state'])) {
     $token_url = "https://graph.facebook.com/oauth/access_token?"
       . "client_id=" . $app_id . "&redirect_uri=" . urlencode($my_url)
       . "&client_secret=" . $app_secret . "&code=" . $code;

     $response = file_get_contents($token_url);
     $params = null;
     parse_str($response, $params);

     $_SESSION['access_token'] = $params['access_token'];

     $graph_url = "https://graph.facebook.com/me?access_token=" 
       . $params['access_token'];

     $user = json_decode(file_get_contents($graph_url));
     echo("Hello " . $user->name);
   }
   else {
     echo("The state does not match. You may be a victim of CSRF.");
   }
?>