public String processingGetTopLevelGroupRequest() throws IOException, KeyHandledException {
    debug("Entering the processingGetTopLevelGroupRequest method");
    
    String jsonFormatted = "";
    CloseableHttpClient httpclient = HttpClients.createDefault();
    try {

      Date now = new Date();
      DateFormat df = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z");
      df.setTimeZone(TimeZone.getTimeZone("GMT"));
      String date = df.format(now);
      
      String dataToSign = "(request-target): get " + gatewayurl
          + "groups\n" + "host: " + gatewayhost + "\n" + "date: "
          + date;
      
      String hmac = generateAuthHeader(dataToSign, apisecret);
      
      String authorisation = "Signature keyId=\""
          + apikey
          + "\",algorithm=\"hmac-sha256\",headers=\"(request-target) host date\",signature=\""
          + hmac + "\"";
      debug("dataToSign is......" + dataToSign);
      debug("hmac is......" + hmac);
      
      HttpGet httpGet = new HttpGet(httpsUrlForGroups);      
      httpGet.addHeader("Authorization", authorisation);
      httpGet.addHeader("Cache-Control", "no-cache");
      httpGet.addHeader("date", date);
      
      //--------  Calling GET method -------------
      CloseableHttpResponse response = httpclient.execute(httpGet);
      //------------------------------------------
      
      try {
        
        HttpEntity entity = response.getEntity();
        debug("response.getStatusLine is.........." + response.getStatusLine());

        String json = EntityUtils.toString(entity);
        ObjectMapper mapper = new ObjectMapper();

        Object jsonObj = mapper.readValue(json, Object.class);
        jsonFormatted = mapper.writerWithDefaultPrettyPrinter()
            .writeValueAsString(jsonObj);
        debug("json is..........." + jsonFormatted);

        EntityUtils.consume(entity);
        
      } finally {
        httpclient.close();
      }
      
    } finally {
      httpclient.close();
    } 
    
    debug("Leaving the processingGetTopLevelGroupRequest method");
    return jsonFormatted;
  } 
  
  /**
   * This method is using for generate the Auth Header
   * 
   * @param dataToSign
   * @param secret
   * @return
   * @throws KeyHandledException 
   */
  // TODO:: it should be moved in a specific Helper class
  public static String generateAuthHeader(String dataToSign, String secret) throws KeyHandledException {

    String hash = "";
    try {
      Mac sha256_HMAC = Mac.getInstance("HmacSHA256");
      SecretKeySpec secret_key = new SecretKeySpec(secret.getBytes(), "HmacSHA256");
      sha256_HMAC.init(secret_key);
      hash = Base64.encodeBase64String(sha256_HMAC.doFinal(dataToSign.getBytes()));
    } catch (Exception e) {
      throw new KeyHandledException(ErrorCodesEnum.GENERIC_ERROR, e.getMessage());
    }
    return (hash);
  }