RefreshToken Not getting send back after I get new token google sheets API

Question

I am using the google sheets API with PHP and followed the quick start guide that can be found over here https://developers.google.com/sheets/quickstart/php

When I do authorize properly and store the follow json file in a speicfied path

{
  "access_token": "xxxxxxx",
  "token_type": "Bearer",
  "expires_in": 3600,
  "refresh_token": "xxxxxx",
  "created": 1472731452
}

After this expires the following gets triggered in my code

if ($client->isAccessTokenExpired()) {
    $client->fetchAccessTokenWithRefreshToken(
        $client->getRefreshToken()
    );

    $this->filesystem
        ->put(
            self::CREDENTIALS,
            json_encode($client->getAccessToken())
        );
}

Now my issue is when that code gets triggered it will update my file to something like the following.

{
  "access_token": "xxxxxxx",
  "token_type": "Bearer",
  "expires_in": 3600,
  "created": 1472731452
}

As you can see there is no refresh token anymore. When this token expires I start getting the following error

[LogicException]
refresh token must be passed in or set as part of setAccessToken

Which is perfactly understandable because I don't have the refresh token there anymore.

My question is why is the refresh token getting removed? I am call the same methods as the one in the quick start guide https://developers.google.com/sheets/quickstart/php

I am talking specificaly about this part in the guide

// Refresh the token if it's expired.
if ($client->isAccessTokenExpired()) {
  $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
  file_put_contents($credentialsPath, json_encode($client->getAccessToken()));
}

Answer 1

Your refresh token expired because the lifespan set in your code was 3600 seconds only/1 hour.

{
"access_token": "xxxxxxx",
"token_type": "Bearer",
"expires_in": 3600, //refresh_token good for 1 hour
"refresh_token": "xxxxxx",
"created": 1472731452
}

Using a refresh token

A refresh token is obtained in offline scenarios during the first authorization code exchange. In these cases, your application may obtain a new access token by sending a refresh token to the Google OAuth 2.0 Authorization server.

To obtain a new access token this way, your application sends an HTTPS POST request to https://www.googleapis.com/oauth2/v4/token. The request must include the following parameters:

Such a request will look similar to the following:

POST /oauth2/v4/token HTTP/1.1
Host: www.googleapis.com
Content-Type: application/x-www-form-urlencoded

client_id=8819981768.apps.googleusercontent.com&
client_secret={client_secret}&
refresh_token=1/6BMfW9j53gdGImsiyUH5kU5RsR4zwI9lUVX-tqf8JXQ&
grant_type=refresh_token

Check this SO thread for additional reference. Hope this helps!