public function updateWebhook($identifier, $newUrl = null, $newIdentifier = null) {
        $putData = [
            'url'        => $newUrl,
            'identifier' => $newIdentifier
        ];
        $response = $this->blocktrailClient->put("webhook/{$identifier}", null, $putData, RestClient::AUTH_HTTP_SIG);
        return self::jsonDecode($response->body(), true);
    }