The Oathkeeper proxy is one piece of the puzzle which basically takes incoming HTTP requests, evaluates them on a set of rules (e.g. authentication of credentials used, checking if the user has the right permissions, transforming the session data to a e.g. JWT) and either grants or denies access.
Other services include, for example, ORY Hydra ( https://github.com/ory/hydra ) which is an OAuth2 & OpenID Connect (certification pending) server that you can put "on top" of your existing user management.
While most developers opt to build these systems (permissions, user management) themselves, it is our vision to build a reliable, broadly adopted set of OSS tools that get you started quickly and that scale well as the requirements of your organization change.
Everything we do is build on top of open standards, we do not want to reinvent the wheel (unless nothing exists wrt to open standards). So everything in this ecosystem integrates well with existing systems.
If you have any questions, feel free to ask.
ps: New account because I lost my password and didn't set up a backup email. Stupid me.