code: public String getCrumb(ServletRequest request) {
          String crumb = null;
          if (request != null) {
              crumb = (String) request.getAttribute(CRUMB_ATTRIBUTE);
          }
          if (crumb == null) {
              crumb = issueCrumb(request, getDescriptor().getCrumbSalt());
              if (request != null) {
                  if ((crumb != null) && crumb.length()>0) {
                      request.setAttribute(CRUMB_ATTRIBUTE, crumb);
                  } else {
                      request.removeAttribute(CRUMB_ATTRIBUTE);
                  }
              }
          }
  
          return crumb;
      }
docs: Get a crumb value based on user specific information in the request.
  @param request