code: public function toHeader()
      {
          $first = true;
          $out = 'Authorization: OAuth';
          foreach ($this->parameters as $k => $v) {
              if (substr($k, 0, 5) != "oauth") {
                  continue;
              }
              if (is_array($v)) {
                  throw new TwitterOAuthException('Arrays not supported in headers');
              }
              $out .= ($first) ? ' ' : ', ';
              $out .= Util::urlencodeRfc3986($k) . '="' . Util::urlencodeRfc3986($v) . '"';
              $first = false;
          }
          return $out;
      }
docs: Builds the Authorization: header
  
  @return string
  @throws TwitterOAuthException