public function update($identity, $params = array())
    {
        $path = Util::subUrl(
            '/subscriptions/:identity',
            array(
                
                'identity' => $identity
            )
        );
        if(isset($params['params'])) { 
            $params['body'] = json_encode(array($this->envelope_key => (object)$params['params']));
        
            unset($params['params']);
        }

        
        $response = $this->api_client->put($path, $params);
        

        return $this->getResourceForResponse($response);
    }