code: public static CloseableHttpClient initHttpClient(boolean insecureMode, File ocspCacheFile)
    {
      if (httpClient == null)
      {
        synchronized (HttpUtil.class)
        {
          if (httpClient == null)
          {
            httpClient = buildHttpClient(
                insecureMode,
                ocspCacheFile,
                enableOcspResponseCacheServer());
          }
        }
      }
      return httpClient;
    }
docs: Accessor for the HTTP client singleton.
  
  @param insecureMode  skip OCSP revocation check if true.
  @param ocspCacheFile OCSP response cache file name. if null, the default
  file will be used.
  @return HttpClient object shared across all connections