Google Drive API for PHP - How to connect? - php

Question

I am just trying to connect my PHP with Google API. My aim is to fetch a particular folder's content and show them as feeds in my site. So for a base I am trying to pull the kind of file of my drive. I am struck. Here is my code.
<?php
require_once 'src/Google_Client.php';
require_once 'src/contrib/Google_DriveService.php';
$client = new Google_Client(); $client->setApplicationName("My Application");
$client->setDeveloperKey("<mykey>");
$service = new Google_DriveService($client);
$optParams = array('fields' => 'kind'); $results = $service->files->listFiles($optParams);
foreach ($results['files'] as $item) {
print($item['kind'].'<br>');
}
?>
When I execute this, I get the following error,
Fatal error: Uncaught exception 'Google_ServiceException' with message
'Error calling GET
https://www.googleapis.com/drive/v2/files?fields=kind&key=:
(403) Insufficient permissions for this file' in
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\src\io\Google_REST.php:66
Stack trace: #0
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\src\io\Google_REST.php(36):
Google_REST::decodeHttpResponse(Object(Google_HttpRequest)) #1
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\src\service\Google_ServiceResource.php(177):
Google_REST::execute(Object(Google_HttpRequest)) #2
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\src\contrib\Google_DriveService.php(465):
Google_ServiceResource->__call('list', Array) #3
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\test.php(12):
Google_FilesServiceResource->listFiles(Array) #4 {main} thrown in
C:\xampp\htdocs\ccl\gdapi\google-api-php-client\src\io\Google_REST.php
on line 66
I gave proper key. Kindly help me. Thank you