public function getOAuthHeader($uri, $queryParameters, $httpMethod){
      $this->sign($uri, $queryParameters, $httpMethod);
      foreach($this->oauthParameters as $k => $v){
           $this->oauthParameters[$k] = $k . '="' . rawurlencode($v) . '"';
      }
      return 'OAuth ' . implode(',', $this->oauthParameters);
  }