composer.json

{
  "name": "",
  "type": "project",
  "require": {
    "fproject/php-jwt": "^4.0",
    "league/oauth2-client": "^2.4"
  }
}

login.php

<?php
use Firebase\JWT\JWT;
use Firebase\JWT\JWK;

$config = getConfig();

$client_id = 'client_id';
$client_secret = 'client_secret';
$redirect_uri = 'redirect_uri';

$provider = new \League\OAuth2\Client\Provider\GenericProvider([
  'clientId'                => $client_id,
  'clientSecret'            => $client_secret,
  'redirectUri'             => $redirect_uri,
  'urlAuthorize'            => '_MY_URL_/v1/authorize',
  'urlAccessToken'          => '_MY_URL_/v1/token',
  'urlResourceOwnerDetails' => '_MY_URL_/v1/resource',
  'scopeSeparator'          => ' ',
  'scopes'                  => array('openid', 'profile', 'groups')
]);

if (!isset($_GET['code'])) {
  $authorizationUrl = $provider->getAuthorizationUrl();
  $_SESSION['oauth2state'] = $provider->getState();

  header('Location: ' . $authorizationUrl);
  exit;

} elseif (empty($_GET['state']) || (isset($_SESSION['oauth2state']) && $_GET['state'] !== $_SESSION['oauth2state'])) {

  if (isset($_SESSION['oauth2state'])) {
      unset($_SESSION['oauth2state']);
  }
  exit('Invalid state');

} else {

  try {
      $accessToken = $provider->getAccessToken('authorization_code', [
          'code' => $_GET['code']
      ]);
      $id_token = $accessToken->getValues()['id_token'];
      $keysPayload = http('_MY_URL_/v1/keys?client_id='.$client_id);
      $jwk = JWK::parseKeySet($keysPayload);
      $jwt = JWT::decode($id_token, $jwk, array('RS256'));
      print_r($jwt);
      die();
  } catch (\League\OAuth2\Client\Provider\Exception\IdentityProviderException $e) {
      exit($e->getMessage());
  }

}