OAUTH2 for Bufferapp API

BufferAppCi.php

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Thirdparty extends CI_Controller {
    //bufferapp application token
    private $access_token = ''; 
    private $client_id = '';
    private $client_secret = '';
    private $callback_url = 'thirdparty/auth/';
    private $token_url  = 'https://api.bufferapp.com/1/oauth2/token.json';


    // Create Post Url
    private $create_url = 'https://api.bufferapp.com/1/updates/create.json?access_token=';

    // Media Attributes WIP
    private $media = 'http://bufferapp.com';

    // Place holder for msgs to be buffered
    private $queue = array();

    function __construct(){
        parent::__construct();
        $this->load->library('session');
        $this->load->model('thirdparty_model');
    }

    // Authenticate buffer account for user
    public function auth(){
        switch ($this->session->userdata('stage')) {
            case 2:
                // Store Code
                $this->session->set_userdata(array('code' => $this->input->get('code')));
                $this->session->set_userdata(array('stage' => 3));
                header('Location: '.base_url() . $this->callback_url);
                break;

            case 3:
                $post_data = array(
                        'client_id' => urlencode($this->client_id),
                        'client_secret' => urlencode($this->client_secret),
                        'callback_url' => urlencode(base_url() . $this->callback_url),
                        'code' => urlencode($this->session->userdata('code')),
                        'grant_type' => 'authorization_code'
                    );

                // Initializing curl
                $ch = curl_init($this->token_url);

                // Setting curl options
                curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type: application/json'));
                curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data );

                // Getting results
                $this->result =  curl_exec($ch); // Getting jSON result string
                $this->session->set_userdata(array('stage' => 4));


                // // Get profile data
                $data = file_get_contents('https://api.bufferapp.com/1/profiles.json?access_token=' . $this->access_token);

                break;

            default: // Stage 1
                header( "Location: " . 'https://bufferapp.com/oauth2/authorize?client_id='.$this->client_id.'&redirect_uri='.base_url() . $this->callback_url.'&response_type=code'); // Send Request
                $this->session->set_userdata(array('stage' => 2));
                break;
        }
    }

    // store user token for buffer account
    function storeProfileAuth($data = array()){
        $this->thirdparty_model->storeProfileAuth($data);
    }

}

/* End of file thirdparty.php */
/* Location: ./application/modules/thirdparty/controllers/thirdparty.php */