Facebook Application From Scratch – 2

This is second part of our Facebook Application Development from Scratch series. You may read part one of the series here. In this part we will learn, how to get authentication for your Facebook Applications. More specifically, we will learn:

• Creating an instance of a PHP Class
• Getting session information of Facebook logged-in user
• Getting User ID of Facebook User
• Getting login URL for authentication purpose
• Using FBML redirect tag

What you need?

In order to develop Facebook Application, we need a client library. Client library is a PHP class which offers us to talk to Facebook APIs in an easy manner. Download Facebook client library from:

http://github.com/facebook/php-sdk/blob/master/src/facebook.php

Start the process!

Create a folder named ‘fb’ in your application folder and move this facebook.php file into the ‘fb’ folder. Create a file fb.inc.php in your ‘fb’ folder and insert below code in it:

<?php

require 'facebook.php';

define('APP_ID','xxxxxxxxxx');
define('SECRET_KEY', 'xxxxxxxxxx');
define('CANVAS_PAGE', 'http://apps.facebook.com/shareacake/');
define('CANVAS_URL', 'http://www.techmug.com/demo/FBFromScratchSeries/');

// Create our Application instance.
$facebook = new Facebook(array(
 'appId'  => APP_ID,
 'secret' => SECRET_KEY,
 'cookie' => true,
));

//Get current user's Facebook session
$session = $facebook->getSession();

// Session based API call.
if ($session) {
 try {
 $uid = $facebook->getUser();
 } catch (FacebookApiException $e) {
 error_log($e);
 }
}

// login or logout url will be needed depending on current user state.
if ($uid) {
 //Do nothing
} else {
 $params = array(
 'next'          =>    CANVAS_PAGE,
 'cancel_url'    =>    CANVAS_PAGE,
 'fbconnect'     =>    0,
 'canvas'        =>    1,
 'req_perms'     =>    ''
 );

 $loginUrl = $facebook->getLoginUrl($params);

 echo '<fb:redirect url="' . $loginUrl . '"/>';
}

?>

Change Application ID and Secret Key of your own. We got these keys in our first episode of this series. Above code is enough for Facebook Application authentication.

Create a file outside the ‘fb’ folder and name it index.php. Include the above file (fb.inc.php) in this newly created index.php file using below code.

<?php
require 'fb/fb.inc.php';
?>

Finally upload all the files to your server to test the application (At CANVAS_URL).

Code Explanation

In the beginning we include Facebook client library class. After this we define 4 Constants to be used in our application.  Then we create an instance of Facebook Class with $facebook object.

After creating an instance, we use our newly created object to get current user’s session by using getSession() method of Facebook Class. If our code finds a session, we try to get current logged-in  user’s Facebook ID. We use getUser() method to acquire currently logged-in user’s ID.

At the moment we will not be able to get information about user, because he has not authenticated our application yet. In the result $uid will not be created.

Now, we move forward to authentication process. We check if we have $uid variable available or not. If this variable is not set yet, we try to get the login URL of our application. We start with creating an array named $params. keys inside this array are the hub of our authentication process. Below is the explanation of used keys:

For all available additional or extended permissions, please visit – http://developers.facebook.com/docs/authentication/permissions

Now its time to put our $params array in to getLoginUrl() method. At this point we have the login url, where user can actually authenticate our application. We use redirect tag of FBML(Facebook Markup Language) to send the user to authentication page.

At the authentication page, user has two options – Allow and Don’t Allow. Once user clicks on Allow button, our application will be authenticated by user. That was all about getting authentication for your Facebook Application.

Since, our application has been authenticated, we can use different API methods to get needful data. To read more about Facebook API and available methods, please visit – http://developers.facebook.com/docs/api

To see a demo of above code, visit our application at:

http://apps.facebook.com/shareacake/

Once you authenticate the application, you will see some information about you. That’s the thing we will learn in next episode…Cheers!

What’s next?

In the next episode, we will get user data using Facebook API. We will also display some cakes to be shared and we will also talk about that what can be achieved by using Facebook API. So stay tune for your Facebook hunger.

Please feel free to ask, your comments are always welcome. If you like this article, please share it on your favorite website. It may help someone somewhere!