code: private Map<String, String> getHttpHeaders(String restUrl) throws Exception {
          // return if already created...
          if (this.requestHttpHeaders != null)
              return this.requestHttpHeaders;
  
          // ...or initialize with default headers
          Map<String, String> httpHeaders = new HashMap<>();
  
          // content type
          httpHeaders.put("Content-Type", "application/json");
  
          // AuthenticationHelper http header
          if (this.authRequired) {
              AuthenticationHelper authHlp = new AuthenticationHelper(root);
              httpHeaders.putAll(authHlp.getHttpHeaderKey());
          }
  
          return httpHeaders;
      }
docs: Gets HTTP header to use in request.
  
  @param restUrl The REST API URL.
  @return Array containing HTTP headers.