Authentication and authorization is pretty easy to implement with custom Dependencies. Multitenancy can be a layer on top of that depending on how you want to shard your DB tables / separate rows. If you're interested in poking around a little more with auth then this plugin can be a starting place: https://github.com/piercefreeman/mountaineer/tree/1d44cdf1c6...

(In an old commit and stripped out from the current codebase until it has better test coverage and the main codebase is stable)