Google Admin SDK PHP не может создать пользователя. Не авторизован

У меня проблема с реализацией Google Admin SDK на PHP. Это всегда дает ошибку

Fatal error: Uncaught exception 'Google_Service_Exception' with message 'Error calling POST
https://www.googleapis.com/admin/directory/v1/users: (403) Not Authorized to access this
resource/api' in ..\google-api-php-client\src\Google\Http\REST.php on line 79

Вот мой код:

<?php

session_start();
/* * **********************************************
Make an API request authenticated with a service
account.
* ********************************************** */
set_include_path("google-api-php-client/src" . PATH_SEPARATOR . get_include_path());
require_once 'Google/Client.php';
require_once 'Google/Service/Directory.php';

/* * **********************************************
ATTENTION: Fill in these values! You can get
them by creating a new Service Account in the
API console. Be sure to store the key file
somewhere you can get to it - though in real
operations you'd want to make sure it wasn't
accessible from the webserver!
The name is the email address value provided
as part of the service account (not your
address!)
Make sure the Books API is enabled on this
account as well, or the call will fail.
* ********************************************** */
$client_id = 'my_client_id'; //Client ID
$service_account_name = 'email'; //Email Address
$key_file_location = 'key.p12'; //key.p12

if ($client_id == '<YOUR_CLIENT_ID>' || !strlen($service_account_name) || !strlen($key_file_location)) {
echo missingServiceAccountDetailsWarning();
}

$client = new Google_Client();
$client->setApplicationName("appname");
$service = new Google_Service_Directory($client);

/* * **********************************************
If we have an access token, we can carry on.
Otherwise, we'll get one with the help of an
assertion credential. In other examples the list
of scopes was managed by the Client, but here
we have to list them manually. We also supply
the service account
* ********************************************** */
if (isset($_SESSION['service_token'])) {
$client->setAccessToken($_SESSION['service_token']);
}
$key = file_get_contents($key_file_location);
$cred = new Google_Auth_AssertionCredentials(
$service_account_name, array('https://www.googleapis.com/auth/admin.directory.user'), $key
);
$client->setAssertionCredentials($cred);
if ($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion($cred);
}
$_SESSION['service_token'] = $client->getAccessToken();/* * **********************************************
We're just going to make the same call as in the
simple query as an example.
* ********************************************** */

$familyName = filter_input(INPUT_GET, 'familyname');
$givenName = filter_input(INPUT_GET, 'givenname');
$password = filter_input(INPUT_GET, 'password');
$primaryEmail = filter_input(INPUT_GET, 'email');

$user = new Google_Service_Directory_User();
$name = new Google_Service_Directory_UserName();

$name->setFamilyName($familyName);
$name->setGivenName($givenName);

$user->setName($name);
$user->setHashFunction("MD5");
$user->setPrimaryEmail($primaryEmail);
$user->setPassword(hash("md5", $password));

$result = $service->users->insert($user);

Там нет документации, и я очень запутался с этой ошибкой.