Gostaria de acessar o Google Agenda usando a conta de serviço. Este é o meu código:<NUMBER> é substituído pelo valor correto na Google API Console.

<?php

require_once 'googleapi/Google_Client.php';
require_once 'googleapi/contrib/Google_CalendarService.php';

const CLIENT_ID = '<NUMBER>.apps.googleusercontent.com';
const SERVICE_ACCOUNT_NAME  = '<NUMBER>@developer.gserviceaccount.com';
const MY_EMAIL  = '<MY NAME>@gmail.com';
const KEY_FILE = 'privatekey.p12';

$client = new Google_Client();
$client->setClientId(CLIENT_ID);
$client->setApplicationName("<APP NAME>");

$key = file_get_contents(KEY_FILE);
$client->setAssertionCredentials(new Google_AssertionCredentials(
    SERVICE_ACCOUNT_NAME,
    array('https://www.googleapis.com/auth/calendar'),
    $key,
    'notasecret',
    'http://oauth.net/grant_type/jwt/1.0/bearer',
    MY_EMAIL)
);

$cal = new Google_CalendarService($client);
$calList = $cal->calendarList->listCalendarList();

print "<h1>Calendar List</h1><pre>" . print_r($calList, true) . "</pre>";

Quando executo meu código, recebo:

Erro fatal: exceção não capturada 'Google_AuthException' com mensagem 'Erro ao atualizar o token OAuth2, mensagem:' {"error": "access_denied"} '' em /home/www/65683f67e3f0d94b14bba3c945014cda/web/intranet/googleapi/auth/Google_OAuth2.php : 279 Rastreio de pilha: # 0 /home/www/65683f67e3f0d94b14bba3c945014cda/web/intranet/googleapi/auth/Google_OAuth2.php(256): Google_OAuth2-> refreshTokenRequest (matriz) # 1 / home / www / 65683f67e3f0d94b14bba3c945014cda / web / intranet / googleapi /auth/Google_OAuth2.php(209): Google_OAuth2-> refreshTokenWithAssertion () # 2 /home/www/65683f67e3f0d94b14bba3c945014cda/web/intranet/googleapi/service/Google_ServiceResource.php(166): Google_OAuth2-> sign (Object (Google_HttpRequest)) # 3 /home/www/65683f67e3f0d94b14bba3c945014cda/web/intranet/googleapi/contrib/Google_CalendarService.php(154): Google_ServiceResource -> __ call ('list', Array) # 4 / home / www / 65683f67e3f0d94b14bba3c945014cda / web / intranet / testService. php (32): Google_CalendarListServiceResource-> listCalendarList () # 5 {main} lance n em /home/www/65683f67e3f0d94b14bba3c945014cda/web/intranet/googleapi/auth/Google_OAuth2.php na linha 279

Se eu mudar meu código com:

$client->setAssertionCredentials(new Google_AssertionCredentials(
SERVICE_ACCOUNT_NAME,
array('https://www.googleapis.com/auth/calendar'),
$key));

Eu recebi:

(403) Acesso não configurado

o que há de errado aqui?