public static function prepare_tokens($keys, HTTPRequest $request)
    {
        $target = null;
        foreach ($keys as $key) {
            $token = new static($key, $request);
            // Validate this token
            if ($token->reloadRequired() || $token->reloadRequiredIfError()) {
                $token->suppress();
                $target = $token;
            }
        }
        return $target;
    }