php - Using a Service Account, getAccessToken() is returning null -

i running following php code, using client libraries found here: https://code.google.com/p/google-api-php-client/. not errors of code, when call getaccesstoken(), returns null.

i have allowed access service account on personal calendar, , have granted full access project via api console.

any ideas?

require_once 'google-api-php-client/src/google_client.php';  const client_id = 'blahblahblah'; const service_account_name = 'blahblahblah@developer.gserviceaccount.com'; const key_file = 'path/to/privatekey.p12';  $google_client = new google_client(); // created initialized static dependencies $client = new google_oauth2(); // need google_oauth2  $key = file_get_contents(key_file);    $client->setassertioncredentials(     new google_assertioncredentials(         service_account_name,         array('https://www.googleapis.com/auth/calendar'),         $key     ) );  var_dump($client->getaccesstoken()); 

for reason, seemed work:

require_once 'google-api-php-client/src/google_client.php';  const client_id = 'blahblahblah'; const service_account_name = 'blahblahblah@developer.gserviceaccount.com'; const key_file = 'path/to/privatekey.p12'; const calendar_scope = "https://www.googleapis.com/auth/calendar";  $key = file_get_contents(key_file); $auth = new google_assertioncredentials(     service_account_name,     array(calendar_scope),     $key );  $client = new google_client(); $client->setscopes(array(calendar_scope)); $client->setassertioncredentials($auth); $client->getauth()->refreshtokenwithassertion(); $accesstoken = $client->getaccesstoken();  $client->setclientid(client_id); 

if can explain why worked, please edit answer or comment!