private void registerMultifactorFlowDefinitionIntoLoginFlowRegistry() {
        multifactorAuthenticationFlowDefinitionRegistries.forEach(registry -> {
            val flowIds = registry.getFlowDefinitionIds();
            for (val flowId : flowIds) {
                val definition = registry.getFlowDefinition(flowId);
                if (definition != null) {
                    LOGGER.trace("Registering flow definition [{}]", flowId);
                    flowDefinitionRegistry.registerFlowDefinition(definition);
                }
            }
        });
    }
Register flow definition into flow registry.
core/cas-server-core-webflow-mfa-api/src/main/java/org/apereo/cas/web/flow/configurer/AbstractCasMultifactorWebflowConfigurer.java