App_access_token Always Returns False - php

Question

According to the Facebook docs, using App_access_token is as simple as:
$appid = 'xxx';
$secret = 'yyyyyyyyy';
$facebook = new Facebook(array(
'appId' => $appid,
'secret' => $secret,
'cookie' => true,
));
$session = $facebook->getUser()>0;
if($session){
$access_token = 'access_token='.$facebook->getAccessToken();
$app_access_token = file_get_contents("https://graph.facebook.com/oauth/access_token?client_id=$appid&client_secret=$secret&grant_type=client_credentials");
}
My problem is that $access_token is fine but $app_access_token always returns false, what am I doing wrong?
-EDIT-
If I open the app_access_token URL in my browser I can see the access token! It seems to fail the file_get_contents... ?

Answer 1

The file_get_contents could be creating problems, may be due to some php config settings. (Discussion here: file_get_contents returns empty string)
I'll recommend you to use cURL instead, something like that-
function get_content($URL){
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_URL, $URL);
$data = curl_exec($ch);
curl_close($ch);
return $data;
}
echo get_content('http://example.com');
If the problem persists, re-check the values of app_id and secret in the url.

Answer 2

I file_get_contents not working try this :
Enable php ini setting for allow_url_fopen, then restart the server.
Here is the working code :
<?php
$facebook_appid = "facebook_appid"; // Facebook appplication id
$facebook_secret = "facebook_secret"; // Facebook secret id
$redirect_uri = "https://192.168.75.44/facebook_login/fb_login.php"; // return url to our application after facebook login ## should be SAME as in facebook application
//$cancel_url = ""; // redirect url if user denies the facebook login ## should be SAME as in facebook application
$scope = "user_photos,email,user_birthday,user_online_presence,offline_access"; // User permission for facebook
$code = $_REQUEST["code"]?$_REQUEST["code"]:"";
if(empty($code)) {
$_SESSION['state'] = time(); // CSRF protection
$dialog_url = "https://www.facebook.com/dialog/oauth?client_id=". $facebook_appid . "&redirect_uri=" . urlencode($redirect_uri) . "&state=". $_SESSION['state'] . "&scope=".$scope;
header("location:".$dialog_url);
}
if($_SESSION['state'] && ($_SESSION['state'] == $_REQUEST['state'])) {
$token_url = "https://graph.facebook.com/oauth/access_token?". "client_id=" . $facebook_appid . "&redirect_uri=" . urlencode($redirect_uri). "&client_secret=" . $facebook_secret . "&code=" . $code;
$response = #file_get_contents($token_url);
$params = null;
parse_str($response, $params);
echo $params['access_token'];
}
?>