Question

I’m an web developer in Korea and I’m running a fan page on facebook.
and I create a iframe app in facebook.
In this app, The only information I want to know is
if the user liked the page.

So far, I used to do it with the signed request from facebook.
But I Found this page which validate without permissions request

http://www.facebook.com/ITsamsung?sk=app_298897280155645

How is this validation done?

Answer 1

You can use php for this:

<?php

$signedRequestObject = parse_signed_request( $_POST["signed_request"],YOUR_APPLICATION_SECRET );

if ($signedRequestObject["page"]){
    // this means this signed_request was generated on a page
    if ($signedRequestObject["page"]["liked"]){
        // the page was liked
    }
}


//used functions
function parse_signed_request($signed_request, $secret) {
  list($encoded_sig, $payload) = explode('.', $signed_request, 2); 
  $sig = $this->base64_url_decode($encoded_sig);
  $data = json_decode($this->base64_url_decode($payload), true);
  if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
    echo  'Unknown algorithm. Expected HMAC-SHA256 : ';
    return false;
  }
  $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
  if ($sig !== $expected_sig) {
    echo = 'Bad Signed JSON signature!';
    return false;
  }
  return $data;
}

function base64_url_decode($input) {
  return base64_decode(strtr($input, '-_', '+/'));
}

?>