public function makeRequestToken(Response $response)
    {
        parse_str($response->content(), $params);

        $this->validateRequestTokenResponse($params);

        $this->credentials['key'] = $params['oauth_token'];
        $this->credentials['secret'] = $params['oauth_token_secret'];
        $this->credentials['callback_confirmed'] = (isset($params['oauth_callback_confirmed'])) ?
                                                        (boolean) $params['oauth_callback_confirmed'] : null;

        return $this;
    }