php - Need Help on OAuthException Code 2500

Question

I am trying to develop an Facebook application (apps.facebook.com/some_app) using PHP where I need to present some information based on user's music interests. I found that its under "user_likes > games".

My problems are as follows:

• To gain access, I have implemented the oauth dialog method as suggested in API in my index page.

---

$auth_url = "http://www.facebook.com/dialog/oauth?client_id="
            . $app_id . "&redirect_uri=" 
            . urlencode($canvas_page)
            ."&scope=user_likes";

• After successful authorization I come back to index page with "code" as parameters.

---

http://MY_CANVAS_PAGE/?code=some base64 encoded letters

• Firstly I don't know if I need access_token just to read user's music interests but I have tried all the methods suggested. I couldn't move forward from this point
• I have a code like this (in my index page), which redirects for authorization if code parameters is not set.

---

if(empty($code) && !isset($_REQUEST['error'])) {
  $_SESSION['state'] = md5(uniqid(rand(), TRUE)); //CSRF protection
  echo("<script> top.location.href='" . $auth_url . "'</script>");
}

• Currently I am just trying to get user's public information here but with no success. I have tried the signed_request method as suggested but no success

---

$signed_request = $_REQUEST["signed_request"];
list($encoded_sig, $payload) = explode('.', $signed_request, 2);
$data = json_decode(base64_decode(strtr($payload, '-_', '+/')), true);
echo ("Welcome User: " . $data["user_id"]);

• Also tried the code found in http://developers.facebook.com/blog/post/500/

  but I am getting error when trying to get the debug info using

---

print_r($decoded_response);

---

stdClass Object ( [error] => stdClass Object ( [message] => An active 
access token must be used to query information about the current user. 
[type] => OAuthException [code] => 2500 ) ) 

To get user's public info, I have tried also the suggested example in PHP SDK

---

$facebook = new Facebook(array(
'appId'  => MY_APP_ID, //registered facebook APP ID
'secret' => MY_SECRET, //secret key for APP
));

$fb_user = $facebook->getUser();

if($fb_user){
    try {
      $user_profile = $facebook->api('/me');
      echo $user_profile['email'];
    }
    catch(FacebookApiException $e) {
      $fb_user = null;
    }
}

But no success. Can somebody explain me why I am getting this error and how to access the user's music interest properly. Probably I misunderstood the API.

Thanks

Deepak

Answer 1

Error 2500 means you have no access token or an app access token but are trying to access /me/ - 'me' is a placeholder for 'current user or page ID' so won't be valid without an access token for a user or page.

To access the user's list of likes you'll also need the user_likes Permission when authorising them

The most likely causes i've seen for apps not being able to exchange the code for an access token are:

1. The redirect_uri you used is to a folder or server root and is missing a trailing slash (i.e it's http://www.example.com instead of http://www.example.com/)
2. The redirect_uri you used in the first call to the auth dialog wasn't precisely the same as the redirect_uri you used in the call to exchagne the code for an access_token

If your auth flow is broken for some other reason and you can't figure it out from the SDK examples or the Authentication documentation, this could take a while for someone to talk you through because you may be missing some background knowledge necessary to understand their answers