private static List<String> findSelectedRecipients(final RequestContext requestContext,
                                                       final Map<String, CandidateRecipientAddress> recipients) {
        if (recipients == null || recipients.isEmpty()) {
            LOGGER.debug("No selected SMS recipients are found in the request context");
            return List.of();
        }
        val parameters = requestContext.getRequestParameters().asMap();
        return parameters
            .keySet()
            .stream()
            .filter(recipients::containsKey)
            .map(entry -> recipients.get(entry).contact())
            .filter(Objects::nonNull)
            .collect(Collectors.toList());
    }
Event attribute to allow registration of email.
support/cas-server-support-simple-mfa-core/src/main/java/org/apereo/cas/mfa/simple/web/flow/CasSimpleMultifactorSendTokenAction.java