FB PHP authentication

I found this code here http://developers.facebook.com/docs/authentication/

<?php 

   $app_id = "YOUR_APP_ID";
   $app_secret = "YOUR_APP_SECRET";
   $my_url = "YOUR_URL";

   session_start();
   $code = $_REQUEST["code"];

   if(empty($code)) {
     $_SESSION['state'] = md5(uniqid(rand(), TRUE)); //CSRF protection
     $dialog_url = "http://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($_REQUEST['state'] == $_SESSION['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);

     $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.");
   开发者_高级运维}

?>

What I changed was the app id app secret and URL, I created a page with one HTML sentence I uploaded this on Web server and I get error page not found. Can anyone help me with that? Also do I need to include anything?

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What you're trying to do in your code is kind of a workaround for something that already exists. Please use the Facebook PHP SDK for things that you're trying right now. It makes the thing a lot easier and you probably get to your goal in less time.

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You need to use the facebook SDK. Here is the sample tutorial, which works me fine,

http://www.9lessons.info/2011/01/facebook-graph-api-connect-with-php-and.html

I am sure it will fix your issue.

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You should use the Facebook PHP SDK (see on github). It is dead simple to deal with logging users in. Here is how it looks like :

require 'facebook.php';
$facebook = new Facebook(...);

$user = $facebook->getUser();

If the user is logged in, $user will contain his Facebook ID. But it does not mean that you have a valid access token to make API calls : if he just logged out from Facebook, $user will not be null but the access token will not be valid anymore.

One way to check if you have a valid token is actually to try to make a API call :

if ($user) {
  // The user is logged in
  try {
    $facebook->api('/me');
    // Here : API call succeeded, you have a valid access token
  } catch (FacebookApiException $e) {
    // Here : API call failed, you don't have a valid access token
    // you have to send him to $facebook->getLoginUrl()
    $user = null;
  }
} else {
  // The user is not logged
  // you have to send him to $facebook->getLoginUrl()
}

And then, to log in the user or to get a valid access token :

if (!$user) {
  // display link to $facebook->getLoginUrl();
}

You may want to check the example of the Facebook PHP SDK to have the complete flow, it is well documented.

Hope that helps.