code: public function baseURL($httpverb, $url, $params)
     {
         uksort($params, 'strcmp');
  
         return strtoupper($httpverb).'&'.
                  rawurlencode($url).'&'.
                  rawurlencode(http_build_query($params));
     }
docs: Build the signature base url.
  
  @param  string $httpverb
  @param  string $url
  @param  array $params
  
  @return string