Depends on what you mean by maintain. If you use one of the well-supported open source solutions like Keycloak then it is very actively maintained with regular releases, bug fixes, new features (U2F support etc). But of course you need to run your own infrastructure (database, application servers, load balancer, maybe separate infinispan cluster if you want to go wild). If you don't have the operational capacity to do that then maybe a SaaS solution is right for you.
