code: private String validateCookie(HttpServletRequest request) throws UnsupportedEncodingException {
      // Find all the valid cookies associated with the request.
      Cookie[] cookies = request.getCookies();
  
      if (cookies == null) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("No valid cookies associated with the request " + request);
        }
        return null;
      }
      if (LOG.isDebugEnabled()) {
        LOG.debug("Received cookies: " + toCookieStr(cookies));
      }
      return getClientNameFromCookie(cookies);
    }
docs: Validate the request cookie. This function iterates over the request cookie headers
  and finds a cookie that represents a valid client/server session. If it finds one, it
  returns the client name associated with the session. Else, it returns null.
  @param request The HTTP Servlet Request send by the client
  @return Client Username if the request has valid HS2 cookie, else returns null
  @throws UnsupportedEncodingException