default Optional<TenantDefinition> extract(final HttpServletRequest request) {
        val flowId = request != null ? FLOW_URL_HANDLER.getFlowId(request) : StringUtils.EMPTY;
        return extract(flowId);
    }
Extract tenant id from request.

@param request the request
@return the tenant id
api/cas-server-core-api-multitenancy/src/main/java/org/apereo/cas/multitenancy/TenantExtractor.java