$user = wp_get_current_user();
$secret = 'My Secret Key given to me from zendesk when enabling SSO with JWT HERE!';
$jwt_header = array(
    'type' => 'JWT',
    'alg' => 'HS256'
);

$user_name = $user->user_firstname . ' ' . $user->user_lastname;

$jwt_payload = array(
    'iat' => (int) $_GET['timestamp'],
    'jti' =>  (float) $user->ID . microtime(true),
    'name' => trim($user_name),
    'email' => $user->user_email
);

if (!empty($_GET['locale_id']))
    $jwt_payload['locale_id'] = $_GET['locale_id'];

$header_string = base64_encode(json_encode($jwt_header));
$payload_string = base64_encode(json_encode($jwt_payload));
$signature = hash_hmac('sha256', $header_string . '.' . $payload_string, $secret);

$redirect = 'https://heavyocity.zendesk.com/access/jwt?return_to=' . urlencode($_GET['return_to']) . '&jwt=' . $header_string . '.' . $payload_string . '.' . base64_encode($signature);