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anitg 0 Newbie Poster

I am trying to get access toke from FB through Developer App. But I am not able to json_decode the call back response.

If I use the token_url call from browser, it returns the access token. But from within the script it does work.

I searched online and foun that it could be that the Json encoded response must be containg some UTF -8 BOM. So I tried some functions that would strip the response from that. However, I still am not able to get that elusive access token as a variable by json decoding and getting an array.

My code 

<?php
function remove_utf8_bom($data)
{
    $bom = pack('H*','EFBBBF');
    $data = preg_replace("/^$bom/", '', $data);
    return $data;
}                   
                    $token_url = "https://graph.facebook.com/oauth/access_token?"
                        . "client_id=".$config['appId']."&redirect_uri=" . urlencode($config['callback_url'])
                        . "&client_secret=".$config['secret']."&code=" . $_GET['code'];
                    echo $token_url."<br>";                 
                    $ch = curl_init();
                    curl_setopt($ch, CURLOPT_URL, $token_url);
                    curl_setopt ($ch, CURLOPT_RETURNTRANSFER, true);
        //          curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
                    $data = curl_exec ($ch);
                    if(curl_exec($ch) === false) {
                        echo 'Curl error: ' . curl_error($ch);
                    } else 
                    {
                        echo 'Operation completed without any errors<br>';
                    }

//                  $data=file_get_contents($token_url);                    
    //              echo $data."<br>";
                    $data = remove_utf8_bom($data);
//                  echo "<br> DATA : <br>";
    //              var_dump($data);
                    $params = null;
                    $params=json_decode($data,true);
                    print_r ($params)."<br>";
                    $_SESSION['token'] = $params['access_token'];

                    echo "SESSION TOKEN : ".$_SESSION['token']."<br>";
?>

But still it returns NULL

I have been breaking my head and browsing all kinds of forums but could not get any solution.

Thanks in advance if you can put me out of my misery

  • 1 Contributor
  • 0 Replies
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Dani AI

Generated

Most likely causes (from ’s snippet)

  • The OAuth endpoint often returns an URL-encoded query string (e.g. access_token=...&expires=...) rather than JSON, so json_decode() will return NULL.
  • The code calls curl_exec() twice (once into $data, then again inside the if), which re‑runs the request and makes error checking wrong.
  • print_r($params)."&lt;br&gt;" concatenates a non‑string return value and can hide what was actually parsed. Also confirm session_start() ran before writing $_SESSION.

Minimal, reliable fixes

  • Capture and check the single curl_exec() result, then inspect it (var_dump or log).
  • If the response is URL-encoded, use parse_str() to get access_token. If JSON is needed, request it via an Accept header and then json_decode().

Example (minimal):

if (session_status() !== PHP_SESSION_ACTIVE) { session_start(); }

$ch = curl_init($token_url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$data = curl_exec($ch);
if ($data === false) {
  error_log('curl error: ' . curl_error($ch));
  curl_close($ch);
  // handle error
}
curl_close($ch);

parse_str($data, $params);
if (!empty($params['access_token'])) {
  $_SESSION['token'] = $params['access_token'];
}

Extra troubleshooting and cautions

  • Verify the built URL actually uses & (not an HTML-escaped &amp;) and that redirect_uri exactly matches the app settings.
  • Inspect the raw $data for error/error_description.
  • To force JSON responses, add an Accept: application/json header to the request or use the official Facebook PHP SDK to avoid low-level mistakes.
  • Do not disable SSL verification in production; only relax it temporarily for testing if necessary.

These targeted checks typically explain why json_decode() returned NULL and will yield the access token reliably.

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