How to access user data with Google Webmaster Tools API - php

Question

I'm just starting to use the api libraries from google and I'm having some trouble accessing to user data. For experimentation I used code from a previos question in this field.
My code executes a petition for the google search console api but it returns an empty array. I autorized the service account from the admin console (https://developers.google.com/identity/protocols/OAuth2ServiceAccount) so I don't know why doesn't it return anything.
set_include_path(get_include_path() . PATH_SEPARATOR . '$path/google-api-php-client-master/src');
require_once realpath('$path/google-api-php-client-master/src/Google/autoload.php');
$client_id = "my-client-id";
$service_account_name = "my-service-account-name#developer.gserviceaccount.com";
$key_file_location = "privatekey.p12";
$client = new Google_Client();
$client->setApplicationName("WMtools_application");
$service = new Google_Service_Webmasters($client);
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/webmasters.readonly'),
$key
);
try{
$client->setAssertionCredentials($cred);
if ($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion($cred);
}
$_SESSION['service_token'] = $client->getAccessToken();
}catch(Exception $e){
echo "Exception captured", $e->getMessage(), "\n";
}
try{
$results = $service->sites->listSites();
$siteList = $results->siteEntry;
var_dump($siteList);
}catch(Exception $e2){
echo "No results", $e2->getMessage(), "\n";
}

Answer 1

I solved the problem. The case is that i have delegated domain-wide authority to my service account and I didn't include in my petition to the API the user email from whom I want to access the data. To solve It just need to add it to the google_Auth_AssertionCredentials this way:
$cred = new Google_Auth_AssertionCredentials(
$service_account_name,
array('https://www.googleapis.com/auth/webmasters.readonly'),
$key
);
$cred->sub = $service_account_user_email; //example#google.com