Pass parameter to an iframe embedded Fan Page in Facebook

Those who use their on hosting inside an iframe  for Facebook Fan page, there is a mechanism to pass additional parameters to your iframe page if you need to create a deep URL.

A normal Fan page of Facebook would like this:

https://www.facebook.com/apps/application.php?id=xxxxxxxxxx&sk=app_XXXXXX

This Url will call your domain, say example.com inside the iframe to load the page.

Each time the iframe is loaded, Facebook do a POST to this iframe URL with some data which we can use to identify the status of the user, eg, whether the user already liked this page, or any other parameter is passed through the fan page url.

Facebook keep app_data variable for developers to pass additional parameters to your iframe page.

eg: https://www.facebook.com/apps/application.php?id=xxxxxxxxxx&sk=app_XXXXXX&app_data=mydata

To retrieve this information, in PHP, use can use the following code:

<?php

if(isset($_REQUEST["signed_request"]))
{

$signed_request = $_REQUEST["signed_request"];
// $_POST also work, but better with $_REQUEST

list($encoded_sig, $payload) = explode(‘.’, $signed_request, 2);

$data = json_decode(base64_decode(strtr($payload, ‘-_’, ‘+/’)), true);

if(isset($data['app_data']))
{
$mydata = $data['app_data']; //here you can get the value you passed
}
}

?>

Check my article here  to see how you can get the ‘like’ status using PHP

Courtesy: From various online sources

Thanks
Sajith