Using Facebook PHP SDK 3 with CodeIgniter 2.1

To access the Facebook API, there exists the Facebook PHP SDK to simplify the process. I needed Facebook OAuth in one of my projects using CodeIgniter but had some hard time trying to get it done. I faced a lot of errors, the main one though was that: getUser always returns 0. I found out that this is pretty much popular on stackoverflow and other websites – each proposing different solution. In this post, I try to organize all the steps and collect them in one place. References and downloads are provided at the end of the post.

Facebook App

  1. Before starting, make sure you create a new App.
  2. Get the APP ID and APP Secret.
  3. After creating your App, click Edit Settings or Edit App.
  4. In the basic info, add your domain name in the App domain.
  5. In the “select how your app integrates with Facebook” click on website and add the same domain you added in step 4 but with http:// as prefix.
  6. If you want to test locally, try creating a Virtual Host.

Installing

  1. Download the Facebook PHP SDK.
  2. Download CodeIgniter.
  3. Extract CodeIgniter.
  4. Extract the Facebook SDK and
    1. Rename facebook.php to Facebook.php
    2. add the following at the beginning of the Facebook.php file right after the php opening tag.
      if ( ! defined('BASEPATH')) exit('No direct script access allowed');
    3. Copy the 3 files in the Facebook SDK extracted directory to application/libraries in CodeIgniter.
  5. In CodeIgniter, create a file facebook.php in application/config directory with the following content (make sure to add your application Id and secret key of the Facebook app):
     <?php
     $config['appId'] = 'YOUR APP ID';
     $config['secret'] = 'YOUR SECRET KEY';
    ?>
    
  6. Open your application/config/config.php file and make sure $config['allow_get_array'] is set to true.

Using OAuth

In OAuth, the procedure is the following:

  1. The user clicks on a sign in link on your website.
  2. User is redirected to Facebook, enter his credentials, authorize your app.
  3. Facebook then redirects the user back to your application with data.

Create a controller, say Main Controller. In your controller’s constructor add the following code:

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

class Main extends CI_Controller {

	public function Main(){
		parent::__construct();
		parse_str( $_SERVER['QUERY_STRING'], $_REQUEST );
		$CI = & get_instance();
$CI->config->load("facebook",TRUE);
$config = $CI->config->item('facebook');
$this->load->library('Facebook', $config);
	}

	function index(){
		// Try to get the user's id on Facebook
		$userId = $this->facebook->getUser();

		// If user is not yet authenticated, the id will be zero
		if($userId == 0){
			// Generate a login url
			$data['url'] = $this->facebook->getLoginUrl(array('scope'=>'email'));
			$this->load->view('main_index', $data);
		} else {
			// Get user's data and print it
			$user = $this->facebook->api('/me');
			print_r($user);
		}
	}

}

?>

Create a view, called main_index.php in your views directory.


<a href="<?php echo $url; ?>">Click here to login</a>

In the constructor, the parse_str function is called to copy the variables sent by Facebook to the $_REQUEST var so that the Facebook SDK can do its checks. This step is required because CodeIgniter has its own special input class that manipulates $_GET, $_POST, $_COOKIE, and so on. After that, the Facebook configuration is loaded and used to initialize the Facebook SDK (or we can call it the Facebook library by now).

In the index function, we first check whether the user is already authenticated by trying to get his user id. If the id is zero, that means he is not authenticated and we need to authenticate. This is done by generating a link, getLoginUrl(), and passing it to the view so that the user clicks and authenticate. The array passed to the getLoginUrl() specifies the scope. By default, the getLoginUrl() will cause the user to authenticate our application to get only his basic information. In this example, I assume we want his email as well and therefore I pass it as scope to the getLoginUrl() function.

If the user is authenticated, we get the user’s data and print it. You can read more about that here.

Download

Here is the application folder with everything in this post. Click here to download it.

References

http://stackoverflow.com/questions/9454238/using-facebook-php-sdk-3-x-to-register-login-user-with-codeigniter-2-1-0

http://stackoverflow.com/questions/4478525/is-there-proper-codeigniter-library-to-work-with-facebook-php-sdk

https://developers.facebook.com/docs/reference/php/

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