Micro-service user access gateways?

What solutions exist for user access flow ( registration, login, and sessions) close to the front end (nginx reverse proxy) of the web services stack for microservice architectures?

Is there anyway to keep user access built into a primary nginx reverse proxy server by way of custom modules?

My assumption is the initial reverse proxy can handle user access and life cycle management but what specific solutions exist to best handle user access to micro-services?