How to get google client with php by cookie ref https://github.com/waarneembemiddeling/php-google-analytics-cookie-parser

get_google_client.php

function getGAClient() { 
  $result = explode('.', $_COOKIE['_ga'], 3); 
  $count = count($result);
  if ($count == 3) { 
    list($version, $depth, $clientId) = $result; 
  } else { 
    return false; 
  }
  
  return $clienId;
  
}