Get user id in case Signed Request - Facebook - facebook

Question

I know it might be duplicate question but please help. I have created a app and installed it on my Facebook page. My issue when I authenticate it using authentication method I got the user id... But when I go through proper signed request method (i.e. When I login with facebook site only.) I don't get user. how can I get userid in case of signed request that When I login using facebook site.
My signed request.
$facebook = new Facebook(array(
'appId' => '****',
'secret' => '****',
'cookie' => true,
));
echo 'User ID :- ' . $user = $facebook->getUser();
$signed_request = $facebook->getSignedRequest();
echo '<pre>';
print_r($signed_request);
echo '</pre>';
User ID :- 0
Array (
[algorithm] => HMAC-SHA256
[issued_at] => 1372676199
[page] => Array
(
[id] => 544896778905441
[liked] =>
[admin] => 1
)
[user] => Array
(
[country] => in
[locale] => en_US
[age] => Array
(
[min] => 21
)
)
)
How can I get User id.

Answer 1

** EDIT **
As of a few months ago (Dec 2014) Facebook no longer allows Like-Gating content. I guess that's why someone is going around placing negative votes and links to their own answers. So the below is no longer valid
There is a difference between getting a signed_request for a user who has authorised an app, which is your first case and getting the user id from a signed request on a page app. In the second example you can test if a user likes your page, but you can't get the specific user id. They are just interacting with your page - yes they may be logged into Facebook, but they haven't explicitly authorised your app. I presume this is what you mean by "login with Facebook site only"
If you look at https://developers.facebook.com/docs/reference/login/signed-request/ you will see it states
Some fields and values, the user_id and oauth_token for example will only be passed if the user has logged into your app.
They may be logged into Facebook, but not have logged in/authorised your app

Answer 2

You can follow the instruction on how to decode the signed request here
https://developers.facebook.com/docs/facebook-login/using-login-with-games#parsingsr
OR
You can use the service that I created. It will return decoded signed request :)
https://websta.me/fbappservice/parseSignedRequest/<concat signed request here>
//angularjs
you may get it via $http.jsonp(url);
//jquery // refer to jquery docs on getting jsonp requests
$.getJSON( url, {
format: "json"
})