docs: private String getCertFromHeader(final HttpServletRequest request) {
          val certHeaderValue = request.getHeader(sslClientCertHeader);
          if (StringUtils.isBlank(certHeaderValue)) {
              return null;
          }
  
          if ("(null)".equalsIgnoreCase(certHeaderValue)) {
              return null;
          }
          return StringUtils.trim(certHeaderValue);
      }