code: public String handle(final Exception e, final RequestContext requestContext) {
          val messageContext = requestContext.getMessageContext();
  
          if (e instanceof AuthenticationException) {
              return handleAuthenticationException((AuthenticationException) e, requestContext);
          }
  
          if (e instanceof AbstractTicketException) {
              return handleAbstractTicketException((AbstractTicketException) e, requestContext);
          }
  
          LOGGER.trace("Unable to translate errors of the authentication exception [{}]. Returning [{}]", e, UNKNOWN);
          val messageCode = this.messageBundlePrefix + UNKNOWN;
          messageContext.addMessage(new MessageBuilder().error().code(messageCode).build());
          return UNKNOWN;
      }
docs: Maps an authentication exception onto a state name.
  Also sets an ERROR severity message in the message context.
  
  @param e              Authentication error to handle.
  @param requestContext the spring  context
  @return Name of next flow state to transition to or {@value #UNKNOWN}