$client = new Google_Client(); $client->setClientId('YOUR_CLIENT_ID'); $client->setClientSecret('YOUR_CLIENT_SECRET'); $client->setRedirectUri('YOUR_REDIRECT_URI'); $client->setScopes(array('email', 'profile')); // Authenticate client if (isset($_GET['code'])) { $token = $client->fetchAccessTokenWithAuthCode($_GET['code']); // Save refresh token to database $refresh_token = $client->getRefreshToken(); // Store refresh token store_refresh_token($refresh_token); } else { // Redirect to authentication page $auth_url = $client->createAuthUrl(); header('Location: ' . filter_var($auth_url, FILTER_SANITIZE_URL)); }In this example, the code retrieves the refresh token after authenticating with Google API Authorization. The refresh token is then stored in a database for later use. The package library for this function is the Google API Client Library for PHP, which can be installed using Composer or downloaded from the GitHub repository.