Error validate an ID token in PHP - Google API - php

Question

I am using the following example backend-auth Google
<?php
require_once 'Google/vendor/autoload.php';
$CLIENT_ID = "xxxxxxxxxx";
// Get $id_token via HTTPS POST.
$client = new Google_Client(['client_id' => $CLIENT_ID]); // Specify the CLIENT_ID of the app that accesses the backend
$payload = $client->verifyIdToken($id_token);
if ($payload) {
$userid = $payload['sub'];
// If request specified a G Suite domain:
//$domain = $payload['hd'];
} else {
// Invalid ID token
}
?>
I have already created the credentials, API, and OAUTH2
API_KEY: AIzaAsDfGuYn6nk9761kvnwMxns-PPeO1Ka1YsA
CLIENT_ID: 15123456862-94jrd0d2lis29lbl6dekpk0fp4otgm8r.apps.googleusercontent.com
CLIENT_SECRET: qertf3l3UfgdhjiWEREZI8xN
But it generates the following error:
Notice: Undefined variable: id_token in C:\Adsense\index.php on line 10
Fatal error: Uncaught LogicException: id_token must be passed in or set as part of setAccessToken in C:\Adsense\Google\vendor\google\apiclient\src\Client.php:784 Stack trace: #0 C:\Adsense\index.php(10): Google\Client->verifyIdToken(NULL) #1 {main} thrown in C:\Adsense\Google\vendor\google\apiclient\src\Client.php on line 784
I have searched this forum in the google documentation and in the google console panel but I cannot find a fixed token or how to create it, I cannot find references
https://oauth2.googleapis.com/tokeninfo?id_token=XXXXX

Answer 1

It's a bit of an old post, but for anyone like me and the OP struggling with this, it's actually quite a simple solution.
The example code has a commented out line that reads
// Get $id_token via HTTPS POST.
You actually have to write this code. Using the worked examples from Google, the JavaScript function passes the authentication token as idtoken.
$id_token = $_POST['idtoken'];
Will do the trick. You'll probably want to perform some basic error checking, for example,
if (isset($_POST['idtoken'])){
$id_token = $_POST['idtoken'];
$payload = $client->verifyIdToken($id_token);
...