<?php
/**
 * Get an OAuth2 token from Google.
 * * Install this script on your server so that it's accessible
 * as [https/http]://<yourdomain>/<folder>/get_oauth_token.php
 * e.g.: http://localhost/phpmail/get_oauth_token.php
 * * Ensure dependencies are installed with 'composer install'
 * * Set up an app in your Google developer console
 * * Set the script address as the app's redirect URL
 * If no refresh token is obtained when running this file, revoke access to your app
 * using link: https://accounts.google.com/b/0/IssuedAuthSubTokens and run the script again.
 * This script requires PHP 5.4 or later
 * PHP Version 5.4
 */

require 'vendor/autoload.php';

session_start();

//If this automatic URL doesn't work, set it yourself manually
$redirectUri = isset($_SERVER['HTTPS']) ? 'https://' : 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'];
//$redirectUri = 'http://localhost/phpmailer/get_oauth_token.php';

//These details obtained are by setting up app in Google developer console.
$clientId = 'RANDOMCHARS-----duv1n2.apps.googleusercontent.com';
$clientSecret = 'RANDOMCHARS-----lGyjPcRtvP';

//Set Redirect URI in Developer Console as [https/http]://<yourdomain>/<folder>/get_oauth_token.php
$provider = new League\OAuth2\Client\Provider\Google(
    array(
        'clientId' => $clientId,
        'clientSecret' => $clientSecret,
        'redirectUri' => $redirectUri,
        'scopes' => array('https://mail.google.com/'),
        'accessType' => 'offline'
    )
);

if (!isset($_GET['code'])) {
    // If we don't have an authorization code then get one
    $authUrl = $provider->getAuthorizationUrl();
    $_SESSION['oauth2state'] = $provider->getState();
    header('Location: ' . $authUrl);
    exit;
// Check given state against previously stored one to mitigate CSRF attack
} elseif (empty($_GET['state']) || ($_GET['state'] !== $_SESSION['oauth2state'])) {
    unset($_SESSION['oauth2state']);
    exit('Invalid state');
} else {
    // Try to get an access token (using the authorization code grant)
    $token = $provider->getAccessToken(
        'authorization_code',
        array(
            'code' => $_GET['code']
        )
    );

    // Use this to get a new access token if the old one expires
    echo 'Refresh Token: ' . $token->getRefreshToken();
}