Are you sure this is not possible? Because Wordstream actually does this job. When you log in to them with your Google Ads account, they can manage your campaigns.
Actually, I succeeded partially in the link below, but for some reason I cannot get access to the account. Where is my fault I'm trying to figure it out.
require 'google-api/vendor/autoload.php';
use Google\Auth\OAuth2;
use Google\AdsApi\AdWords\AdWordsServices;
use Google\AdsApi\AdWords\AdWordsSessionBuilder;
use Google\AdsApi\AdWords\v201809\cm\CampaignService;
use Google\AdsApi\Common\OAuth2TokenBuilder;
session_start();
$oauth2 = new OAuth2([
'redirectUri' => 'XXXXX',
'clientId' => 'XXXXXX,
'clientSecret' => 'XXXXX',
'refresh_token' => XXXXX'
]);
if(!isset($_GET['code'])){
$oauth2->setState(sha1(openssl_random_pseudo_bytes(1024)));
$_SESSION['oauth2state'] = $oauth2->getState();
$config = [
'access_type' => 'offline',
'prompt' => 'consent',
];
header('Location: ' . $oauth2->buildFullAuthorizationUri($config));
exit;
} elseif (empty($_GET['state']) || ($_GET['state'] !== $_SESSION['oauth2state'])){
unset($_SESSION['oauth2state']);
exit('Invalid state.');
} else {
$oauth2->setCode($_GET['code']);
$authToken = $oauth2->fetchAuthToken();
$refreshToken = $authToken['refresh_token'];
$path = "xxxxxx/google-api/vendor/adsapi_php.ini";
$session = (new AdWordsSessionBuilder())
->fromFile($path)
->withOAuth2Credential($oauth2)
->build();
$adWordsServices = new AdWordsServices();
$campaignService = $adWordsServices->get($session, CampaignService::class);
print_r($campaignService);
}