public function getRequestToken($callback_uri = NULL) {

    // set callback_uri
    $this->getOauthPlugin()->setCallbackUri($callback_uri);

    //Get request token
    $response = $this->get($this->getConfig('request_token_path'))->send();
    $request_token = array();
    parse_str($response->getBody(), $request_token);

    // Throw exception if the callback isn't confirmed
    if (!isset($request_token['oauth_callback_confirmed']) || !in_array($request_token['oauth_callback_confirmed'], array(true, "true"))) {
      throw new \Exception("There was an error regarding the callback confirmation");
    }

    // Return RequestToken
    return $request_token;
  }