protected String getTicketGrantingTicket(final RequestContext context) {
        val tgtId = WebUtils.getTicketGrantingTicketId(context);
        if (StringUtils.isBlank(tgtId)) {
            val request = WebUtils.getHttpServletRequestFromExternalWebflowContext(context);
            return ticketGrantingTicketCookieGenerator.retrieveCookieValue(request);
        }
        return tgtId;
    }
Parameter to indicate logout request is confirmed.
support/cas-server-support-actions-core/src/main/java/org/apereo/cas/web/flow/logout/TerminateSessionAction.java