Facebook Authentication using cURL (php)

[SystemFiles]

I'm trying to use cURL to do facebook authentication and here's what I have:\[code\] $url = "https://graph.facebook.com/oauth/access_token"; $postString = "?client_id=$client_id&redirect_uri=$redirect_uri&client_secret=$client_secret&code=$code"; $curl = curl_init(); curl_setopt($curl, CURLOPT_URL, $url); curl_setopt($curl, CURLOPT_FAILONERROR, 1); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); curl_setopt($curl, CURLOPT_FOLLOWLOCATION, 1); //curl_setopt($curl, CURLOPT_POST, 1); curl_setopt($curl, CURLOPT_POSTFIELDS, $postString); $response = curl_exec($curl);\[/code\]but every time it just returns false.I'm pretty new to using cURL so I could be making some beginner mistakes, but I'm confused as to why this isn't working at all.Any help would be greatly appreciated!