putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');

use Google\Auth\ApplicationDefaultCredentials;
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;

// specify the path to your application credentials
putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');

// define the scopes for your API call
$scopes = ['https://www.googleapis.com/auth/drive.readonly'];

// create middleware
$middleware = ApplicationDefaultCredentials::getMiddleware($scopes);
$stack = HandlerStack::create();
$stack->push($middleware);

// create the HTTP client
$client = new Client([
  'handler' => $stack,
  'base_uri' => 'https://www.googleapis.com',
  'auth' => 'google_auth'  // authorize all requests
]);

// make the request
$response = $client->get('drive/v2/files');

// show the result!
print_r((string) $response->getBody());

// create the HTTP client
$client = new Client([
  'base_url' => 'https://www.googleapis.com',
  'auth' => 'google_auth'  // authorize all requests
]);

// create subscriber
$subscriber = ApplicationDefaultCredentials::getSubscriber($scopes);
$client->getEmitter()->attach($subscriber);

use Google\Auth\ApplicationDefaultCredentials;
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;

// specify the path to your application credentials
putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');

// Provide the ID token audience. This can be a Client ID associated with an IAP application,
// Or the URL associated with a CloudRun App
//    $targetAudience = 'IAP_CLIENT_ID.apps.googleusercontent.com';
//    $targetAudience = 'https://service-1234-uc.a.run.app';
$targetAudience = 'YOUR_ID_TOKEN_AUDIENCE';

// create middleware
$middleware = ApplicationDefaultCredentials::getIdTokenMiddleware($targetAudience);
$stack = HandlerStack::create();
$stack->push($middleware);

// create the HTTP client
$client = new Client([
  'handler' => $stack,
  'auth' => 'google_auth',
  // Cloud Run, IAP, or custom resource URL
  'base_uri' => 'https://YOUR_PROTECTED_RESOURCE',
]);

// make the request
$response = $client->get('/');

// show the result!
print_r((string) $response->getBody());

use Google\Auth\CredentialsLoader;
use Google\Auth\Middleware\AuthTokenMiddleware;
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;

// Define the Google Application Credentials array
$jsonKey = ['key' => 'value'];

// define the scopes for your API call
$scopes = ['https://www.googleapis.com/auth/drive.readonly'];

// Load credentials
$creds = CredentialsLoader::makeCredentials($scopes, $jsonKey);

// optional caching
// $creds = new FetchAuthTokenCache($creds, $cacheConfig, $cache);

// create middleware
$middleware = new AuthTokenMiddleware($creds);
$stack = HandlerStack::create();
$stack->push($middleware);

// create the HTTP client
$client = new Client([
  'handler' => $stack,
  'base_uri' => 'https://www.googleapis.com',
  'auth' => 'google_auth'  // authorize all requests
]);

// make the request
$response = $client->get('drive/v2/files');

// show the result!
print_r((string) $response->getBody());

use Google\Auth\ApplicationDefaultCredentials;
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;

// specify the path to your application credentials
putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');

// Provide the ID token audience. This can be a Client ID associated with an IAP application
//    $targetAudience = 'IAP_CLIENT_ID.apps.googleusercontent.com';
$targetAudience = 'YOUR_ID_TOKEN_AUDIENCE';

// create middleware
$middleware = ApplicationDefaultCredentials::getProxyIdTokenMiddleware($targetAudience);
$stack = HandlerStack::create();
$stack->push($middleware);

// create the HTTP client
$client = new Client([
  'handler' => $stack,
  'auth' => ['username', 'pass'], // auth option handled by your application
  'proxy_auth' => 'google_auth',
]);

// make the request
$response = $client->get('/');

// show the result!
print_r((string) $response->getBody());

use Google\Auth\AccessToken;

$auth = new AccessToken();
$auth->verify($idToken);

use Google\Auth\AccessToken;

$auth = new AccessToken();
$auth->verify($idToken, [
  'certsLocation' => AccessToken::IAP_CERT_URL
]);