<?
require_once 'Google/autoload.php';
require_once 'Google/Client.php';
require_once 'Google/Service/YouTube.php';
require_once 'krumo/class.krumo.php';

$client_email = 'Service account email';
$scopes = array(Google_Service_YouTube::YOUTUBE);
$user_to_impersonate = 'The address of my YouTube account';

$private_key = file_get_contents('location of app .p12 file');

if (isset($user_to_impersonate) && $user_to_impersonate != "")
{
  $credentials = new Google_Auth_AssertionCredentials(
      $client_email,
      $scopes,
      $private_key,
      'notasecret',                                 // Default P12 password
      'http://oauth.net/grant_type/jwt/1.0/bearer', // Default grant type
      $user_to_impersonate
  );
}
else
{
  $credentials = new Google_Auth_AssertionCredentials(
      $client_email,
      $scopes,
      $private_key
  );
}

$client = new Google_Client();
try
{
  $client->setAssertionCredentials($credentials);
}
catch (Google_Auth_Exception $e)
{
  die("false:Unable to acquire credentials.");
}

if ($client->getAuth()->isAccessTokenExpired())
{
  try
  {
    $client->getAuth()->refreshTokenWithAssertion();
  }
  catch (Google_Auth_Exception $e)                        //<---- The code fails at this exception when the impersonate code is used
  {
    log_file($e->getMessage(), "../error.log");
    die("false:Token has expired. Unable to refresh.");
  }
}

if (isset($_GET['display']))
{
  krumo($client);
}

$youtube = new Google_Service_YouTube($client);