instagram api get token By php server

gistfile1.txt

<?php

$client_id = <client_id>;
$client_secret = <client_secret>;
$redirect_uri = <redirect_url>;
$scope = 'basic+public_content+comments+relationships+likes';


session_start();
if (isset($_GET['code']) && !empty($_GET['code']) && isset($_SESSION['state']) && !empty($_SESSION['state']) && isset($_GET['state']) && !empty($_GET['state']) && $_SESSION['state'] == $_GET['state']) {

    $context = array(
        'http' => array(
            'method' => 'POST',
            'content' => http_build_query(array(
                'client_id' => $client_id,
                'client_secret' => $client_secret,
                'grant_type' => 'authorization_code',
                'redirect_uri' => $redirect_uri,
                'code' => $_GET['code'],
            )),
        ),
    );

    $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, 'https://api.instagram.com/oauth/access_token');
    curl_setopt($curl, CURLOPT_HEADER, 1);
    curl_setopt($curl, CURLOPT_CUSTOMREQUEST, $context['http']['method']);
    curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_POSTFIELDS, $context['http']['content']);
    curl_setopt($curl, CURLOPT_TIMEOUT, 5);
    $res1 = curl_exec($curl);
    $res2 = curl_getinfo($curl);
    curl_close($curl);
    $json = substr($res1, $res2['header_size']);
    $header = substr($res1, 0, $res2['header_size']);
    $obj = json_decode($json);

    print_r($obj);


} else {
    session_regenerate_id(true);
    $state = sha1(uniqid(mt_rand(), true));
    $_SESSION['state'] = $state;
    header('Location: https://api.instagram.com/oauth/authorize/?client_id=' . $client_id . '&redirect_uri=' . rawurlencode($redirect_uri) . '&scope=' . $scope . '&response_type=code&state=' . $state);
    exit;
}