Facebook API: /oauth/access_token not working - php

Question

I am trying to obtain a user access token from Facebook with the PHP-SDK. The server-side log-in process works great, redirecting to the correct page and providing $code too.
After the redirect (and checking whether $code exists) I then call the following API method to exchange $code for a user token (API parameters are suppressed here):
$fb->api('/oauth/access_token',array(
'client_id' => APP_ID,
'client_secret' => APP_SECRET,
'redirect_uri' => REDIRECT_URI,
'code' => $code
));
$fb_token = $fb->getAccessToken();
echo $fb_token;
Unfortunately, all I get from this script is still the app token. In fact, reducing the script to just the following does not make any difference:
$fb_token_user = $fb->getAccessToken();
echo $fb_token_user;
So I assume it is all about the /oauth/access_token call which for some reason is not working or at least does no action. It does not return any errors either.
I have tried and tested several alternatives, such as the get_file_contents() method suggested in the Facebook tutorial as well as adding additional parameters to the above API call (e.g. type=client_cred and more), but never succeeding.
Does anybody see why the API call is not working? Is it the script or could it be some app setting on Facebook?
Thanks in advance!

Answer 1

Solved! The code in the question is still not working in spite of ever so many threads on this and other communities stating it does (oddly enough it seemed to work for them).
So I figured I had to go back to the file_get_contents() method as explained by Facebook and it turns out this method was previously not working because allow_url_fopen is disabled on my server. Not wanting to undergo the risk of enabling it, I discovered cURL as a work-around.
And here is the working code:
// cURL Load Function
function cURLget ($ch_url) {
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL,$ch_url);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,true);
curl_setopt($ch,CURLOPT_USERAGENT,$_SERVER['HTTP_USER_AGENT']);
$ch_send = curl_exec($ch);
curl_close($ch);
return $ch_send;
};
// Obtain User Token
$fb_token_get = cURLget("https://graph.facebook.com/oauth/access_token"
. "?client_id=" . APP_ID
. "&client_secret=". APP_SECRET
. "&redirect_uri=" . urlencode(REDIRECT_URI)
. "&code=" . $CODE
);
$fb_token_params = null;
parse_str($fb_token_get,$fb_token_params);
// Print Token Data
echo "Token: " . $fb_token_params['access_token']
. "<br />Expires: " . $fb_token_params['expires'];
Thanks to #FabioAntunes for trying to help me with the original code and to #ShawnECarter for his script for the cURL Load Function.

Answer 2

Stumbled upon this problem today too. Seems my PHP SDK (v.3.2.2) offers a function that solves the problem: setExtendedAccessToken(). (Does pretty much the same thing: Calls graph's "/oauth/access_token" and exchanges the old token against a "long-lived" one).