private Long getIfModifiedSinceMs(RestRequest restRequest) {
    if (restRequest.getArgs().get(RestUtils.Headers.IF_MODIFIED_SINCE) != null) {
      return RestUtils.getTimeFromDateString((String) restRequest.getArgs().get(RestUtils.Headers.IF_MODIFIED_SINCE));
    }
    return null;
  }
Fetches the {@link RestUtils.Headers#IF_MODIFIED_SINCE} value in epoch time if present
@param restRequest the {@link RestRequest} that needs to be parsed
@return the {@link RestUtils.Headers#IF_MODIFIED_SINCE} value in epoch time if present
ambry-frontend/src/main/java/com/github/ambry/frontend/AmbrySecurityService.java