code: private function checkHttpsProxyFullUriRequestParam()
      {
          $result = $this->checkConnectivity();
          if ($result !== true) {
              return $result;
          }
  
          if (!extension_loaded('openssl')) {
              return 'You need the openssl extension installed for this check';
          }
  
          $url = 'https://api.github.com/repos/Seldaek/jsonlint/zipball/1.0.0';
          try {
              $this->rfs->getContents('github.com', $url, false);
          } catch (TransportException $e) {
              try {
                  $this->rfs->getContents('github.com', $url, false, array('http' => array('request_fulluri' => false)));
              } catch (TransportException $e) {
                  return 'Unable to assess the situation, maybe github is down ('.$e->getMessage().')';
              }
  
              return 'It seems there is a problem with your proxy server, try setting the "HTTPS_PROXY_REQUEST_FULLURI" environment variable to "false"';
          }
  
          return true;
      }
docs: Due to various proxy servers configurations, some servers can't handle non-standard HTTP "http_proxy_request_fulluri" parameter,
  and will return error 500/501 (as not implemented), see discussion @ https://github.com/composer/composer/pull/1825.
  This method will test, if you need to disable this parameter via setting extra environment variable in your system.
  
  @return bool|string