Google API Insufficient Permissions listing files - php

Question

I am trying to create an app that (using a Drive service account) lists files in a given folder and allows users to search the content of those files. I am getting a 403 Insufficient Permissions error which I cannot explain.
I have edited the code from the Google API PHP Client Example:
$client_id = '[REMOVED]'; //Client ID
$service_account_name = '[REMOVED]'; //Email Address
$key_file_location = 'key.p12'; //key.p12
$client = new Google_Client();
$client->setApplicationName("Client_Library_Examples");
service = new Google_Service_Drive($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/drive',
'https://www.googleapis.com/auth/drive.file'
),
$key
);
$client->setAssertionCredentials($cred);
if ($client->getAuth()->isAccessTokenExpired()) {
$client->getAuth()->refreshTokenWithAssertion($cred);
}
$_SESSION['service_token'] = $client->getAccessToken();
$result = array();
$pageToken = NULL;
do {
try {
$parameters = array();
if ($pageToken) {
$parameters['pageToken'] = $pageToken;
}
$files = $service->files->listFiles($parameters);
$result = array_merge($result, $files->getItems());
$pageToken = $files->getNextPageToken();
} catch (Exception $e) {
echo "<br/>An error occurred: " . $e->getMessage();
$pageToken = NULL;
}
} while ($pageToken);
echo "<pre>";
print_r($result);
echo "</pre>";
echo "<br />Execution completed.";
The exact error message ($e->getMessage() in the catch above) is Error calling GET https://www.googleapis.com/drive/v2/files: (403) Insufficient Permission - I thought the /drive and /drive.file scopes gave me all the permissions I needed?

Answer 1

First, a quick note: You are requesting both the Drive scope and the Drive.File scope. The later is a subset of the former, so there is no need to request it. You should remove 'https://www.googleapis.com/auth/drive.file' line.
As to the insufficient permissions, this is possibility due to incorrect Developer Console configuration. You should double check that both the API and SDK are enabled for this particular project.

Answer 2

I had the same issue. I created a new secret in the Google Developer Console and re-authenticated. This fixed the problem.