Returns a JSON object containing the signed request that Facebook sends to your FB app as a POST variable.

facebookSignedRequestToJSON.php

$req = htmlspecialchars($_POST['signed_request']);
$reqParts = split('\.', $req);
$encodedValue = $reqParts[1];
$encodedValue = preg_replace('/\+/', '-', $encodedValue);
$encodedValue = preg_replace('/\//', '_', $encodedValue);
$pad = strlen($encodedValue) % 4;
if ($pad > 0) {
  $pad = 4 - $pad;
}
$encodedValue = str_pad($encodedValue, $pad, '=');
$result = json_decode(base64_decode($encodedValue));