invoiceninja/app/Libraries/OAuth/Providers/Google.php

<?php

namespace App\Libraries\OAuth\Providers;

use Google_Client;

class Google implements ProviderInterface
{
    public function getTokenResponse($token)
    {
        $client = new Google_Client();

        return $client->verifyIdToken($token);
    }

    public function harvestEmail($payload)
    {
        return $payload['email'];
    }

    public function harvestSubField($payload)
    {
        return $payload['sub']; // user ID
    }

    public function harvestName($payload)
    {
        return $payload['name'];
    }
}