Facebook Graph API: Can't access the authorization token

Question

What I want is to fetch data using of a public page. I tried the documentation, but wasn't able to find that information. Then I googled it and found this Can you get a public Facebook page's feed using Graph API without asking a user to allow? question here at stackoverflow and that perfectly explained what I want to do with PHP. I read in the McNab's answer that I need an app at facebook to fetch that data (to retrieve an access token). I created an app and it took me to the basic settings page where it gave me the AppId and the AppSecret. Now as from the McNab answer, I only need AppId and app secret to get the auth_token, I used the following code, but due to some reason I get false instead of the AuthToken. What am I doing wrong here? I didn't add any further details to the app, is it causing this problem, do I need to add further details to the app or is there anything else causing this?

P.S Also I am trying this on localhost on my PC.

function fetchUrl($url){

 $ch = curl_init();
 curl_setopt($ch, CURLOPT_URL, $url);
 curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
 curl_setopt($ch, CURLOPT_TIMEOUT, 20);

 $feedData = curl_exec($ch);
 curl_close($ch); 

 return $feedData;

}

$profile_id = "100002138417834";

// App info needed for auth.
$app_id = "--------------";
$app_secret = "-=-=-=-=-=-=-=-=-=-=-=-";

$authToken = fetchUrl("https://graph.facebook.com/oauth/access_token?grant_type=client_credentials&client_id={$app_id}&client_secret={$app_secret}");

var_dump($authToken);

UPDATE:

When I did var_dump(curl_error($ch)); (as suggested in the comments), it gave me this error:

string 'SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed' (length=146)

It returning false means the cUrl failed, not so much the FB Api. Is error reporting on? Try `var_dump(curl_error($ch));` after curl_exec — Jaap Moolenaar, Nov 20 '13 at 06:17
If the returned value is `bool(false)` there was an error, so you should use `curl_error($ch)` to find out what it was. Alternatively, use `curl_setopt(CURLOPT_VERBOSE, 1);` to enable debugging. — Ja͢ck, Nov 20 '13 at 06:18
@JaapMoolenaar no. I got busy. I am going to test the error now. — Kamran Ahmed, Nov 20 '13 at 09:13
@JaapMoolenaar please check the question. I've updated it with the error that I am getting. — Kamran Ahmed, Nov 20 '13 at 09:17

score 1 · Accepted Answer · answered Nov 20 '13 at 09:36

1

The ssl certificate is not correctly validated. Curl used to be able do this properly when it was bundled with CA certificates. Either you point curl to the right certificate ( info here http://curl.haxx.se/docs/sslcerts.html ), or disable validating all together.

You can disable ssl certificate validating using:

curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

This is a very common curl problem, the answer to this is probably all over SO ;-)

answered Nov 20 '13 at 09:36

Jaap Moolenaar

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I solved it using my answer to this question, but your answer works as well (plus seems more easy) Thanks :) – Kamran Ahmed Nov 20 '13 at 09:52
Thanks! You have a good way of handling questions and answers. Keep it up :-) – Jaap Moolenaar Nov 20 '13 at 10:10

score 0 · Answer 2 · answered Nov 20 '13 at 09:50

I tried to output the error (thanks to @Jack) and I got this:

string 'SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed' (length=146)

Seemed like a problem with SSL Certificate. So what I did was:

Downloaded a ca bundle from here.
Put that bundle in the same directory where I had this index.php file i.e. the file having the code.
Then set the CURLOPT_CAINFO option using curl_setopt() to point to that file (it must be absolute path).
Refreshed the page and it was working :)
Here is the line to be added:

curl_setopt($ch, CURLOPT_CAINFO, dirname(__FILE__). '/cacert.pem');

And the credit goes to @Jack who helped me in the chat :)

Facebook Graph API: Can't access the authorization token

2 Answers2