google-API-Client returning empty response from google admin sdk

Question

I'm trying to pull users from google admin sdk. I have the following set up:

function

public function getGoogleUsers ()
    {

        putenv('GOOGLE_APPLICATION_CREDENTIALS=' . resource_path('assets/keys/X-X-X-X-X-X-X'));
        $client = new \Google_Client();
        $client->useApplicationDefaultCredentials();
        $client->setApplicationName('X-X-X-X-X');
        $client->setScopes(array(
            'https://www.googleapis.com/auth/admin.directory.group.member.readonly',
            'https://www.googleapis.com/auth/admin.directory.group.member.readonly',
            'https://www.googleapis.com/auth/admin.directory.orgunit.readonly',
            'https://www.googleapis.com/auth/admin.directory.resource.calendar.readonly',
            'https://www.googleapis.com/auth/admin.directory.user.alias.readonly',
            'https://www.googleapis.com/auth/admin.directory.user.readonly',
            'https://www.googleapis.com/auth/admin.directory.userschema.readonly'
        ));
        $client->setAccessType('offline');

        $client->setSubject('X-X-X-X-X');

        $response = new \Google_Service_Directory($client);

        return json_encode($response);
    }

I have set up OAuth 2.0 client IDs, I have enabled domain wide delegation, i have enabled the admin sdk api, i have added permission for the above scopes. But for some reason I keep getting an empty response.