Using Client Secrets with Google API PHP

client_secrets.php

<?php

require_once __DIR__.'/vendor/autoload.php';

// For PHP you will need to define GOOGLE_APPLICATION_CREDENTIALS environment variable and point it to the path of the file
// You do not need to do this for Google App Engine

putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/service-account.json');
$client = new Google_Client();
$client->useApplicationDefaultCredentials();

// Sample call done to the SQL Admin
$sqladmin = new Google_Service_SQLAdmin($client);
$response = $sqladmin->instances
    ->listInstances('examinable-example-123')->getItems();
echo json_encode($response) . "\n";