Cannot refresh token from google api OAuth2 - php

Question

Here is my php script RefreshToken.php
<?php
$url = 'https://accounts.google.com/o/oauth2/token';
$post_data = array(
'code' => 'xxxxxxxx',
'client_id' => 'xxxxxxxxxxx',
'client_secret' => 'xxxxxxxxxxxxx',
'redirect_uri' => 'http://localhost/googleapi/AuthenticationCode.php',
'grant_type' => 'authorization_code',
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);
$token = json_decode($result);
echo $token->refresh_token . "\n";
?>
Run PHP CLI
php -q RefreshToken.php
PHP Notice: Undefined property: stdClass::$refresh_token in /var/www/googleapi/RefreshToken.php on line 20

Answer 1

The refresh_token is not returned by default in Google OAuth2.
The request for an authorization code requires an extra parameter (access_type): then refresh token will be returned with access_token.
Other unusual behaviour: the refresh_token is returned only one time for a user. If, for some reason, refresh_token is lost for that user, then user will need to open Google Account Security Settings page and drop access for your app. And this is not enough: your app will need to pass more one params (approval_prompt equals true) to indicate we're forcing the request for a new refresh_token.
More info: https://developers.google.com/accounts/docs/OAuth2WebServer#offline)