gistfile1.txt

        $client_id = '';
        $client_secret = '';

        $client = new Google_Client();
        $client->setClientId($client_id);
        $client->setClientSecret($client_secret);
        $client->setScopes('https://www.googleapis.com/auth/plus.login');
        $client->setState('offline');
        $plus = new Google_Service_Plus($client);

        $client->authenticate($_POST['token']);
        $token = json_decode($client->getAccessToken());

        $accessToken = $token->access_token;
        $tokenType = $token->token_type;
        $expires_in = $token->expires_in;
        $idToken = $token->id_token;
        $refresh_token = $token->refresh_token;
        $created = $token->created;

        $ticket = $client->verifyIdToken($idToken);
        $userId = null;
        if ($ticket) {
            $data = $ticket->getAttributes();
            $userId = $data['payload']['sub']; // user ID
        }