code: protected Map<String, String> prepareAllowHeaderMap() {
          final Map<String, String> headerMap = new HashMap<String, String>(5);
          headerMap.put("Access-Control-Allow-Origin", prepareAllowOrigin());
          headerMap.put("Access-Control-Allow-Methods", prepareAllowMethods());
          headerMap.put("Access-Control-Max-Age", String.valueOf(prepareMaxAge()));
          headerMap.put("Access-Control-Allow-Headers", prepareAllowHeaders());
          headerMap.put("Access-Control-Allow-Credentials", prepareAllowCredentials());
          return headerMap;
      }
docs: ------------