For reading app_data in the URL and other other things on Facebook

facebook_request.php

<?php

if (!function_exists('facebook_request')) {
	function facebook_request () {
		if (isset($_REQUEST['signed_request'])) {
			if ($request = $_REQUEST['signed_request']) {
				list($encoded_sig, $payload) = explode('.', $request, 2);
				$decoded = base64_decode(strtr($encoded_sig, '-_', '+/'));
				$data	 = base64_decode(strtr($payload, '-_', '+/'));		
				return json_decode($data, true);
			}
		}
	}
}