linkedin oauth cant exchange auth code for access token - php

Question

I am trying to use linkedin to get profile data of users, I get the authorization code from a button on login form that redirects to another page where I want to have some fields that fill with their name and such to create a user or login. I can't exchange the the auth token for an access one with my post. I get bad request or unauthorized responses. it says I am missing the required parameter "client_id", but it is obviously there ... Please take a look, thanks.
$code = $_GET['code'];
$data =array(
"grant_type" =>"authorization_code",
"code"=> $code,
"redirect_uri" => "http:\\localhost\index.php?doctor=linkedin",
"client_id" => "shh",
"client_secret" => "secret"
);
$str_data = json_encode($data);
//echo $str_data;
//function sendPostData($url, $post){
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://www.linkedin.com/oauth/v2/accessToken');
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS,$str_data);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/x-www-form-urlencoded'));
curl_setopt($ch, CURLOPT_HEADERFUNCTION, "HandleHeaderLine");
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$result = curl_exec($ch);
$token = json_decode($result);
var_dump($token);
curl_close($ch); // Seems like good practice
function HandleHeaderLine( $curl, $header_line ) {
echo "<br>".$header_line; // or do whatever
return strlen($header_line);
}

Answer 1

LinkedIn expects ones POSTed field, as a query string. Try changing:
$str_data = json_encode($data);
to:
$str_data = http_build_query($data);
An Example from their documentation :
POST /oauth/v2/accessToken HTTP/1.1
Host: www.linkedin.com
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&code=987654321&redirect_uri=https%3A%2F%2Fwww.myapp.com%2Fauth%2Flinkedin&client_id=123456789&client_secret=shhdonottell
Hope that helps.