@Override
    protected Event doExecuteInternal(final RequestContext requestContext) {
        val registeredService = WebUtils.getRegisteredService(requestContext);
        val failureEval = provider.getFailureModeEvaluator();
        val checkAvailability = Optional.ofNullable(failureEval)
            .map(eval -> eval.evaluate(registeredService, provider) != MultifactorAuthenticationProviderFailureModes.NONE)
            .orElse(true);
        return !checkAvailability || provider.isAvailable(registeredService) ? yes() : no();
    }
Action that will be called as part of the MFA subflow to determine if a MFA provider
is up and available to provide authentications.

@author Travis Schmidt
@since 5.3.4
core/cas-server-core-webflow-mfa-api/src/main/java/org/apereo/cas/web/flow/actions/MultifactorAuthenticationAvailableAction.java