There's a plugin for Sequel::Model that provides ActiveModel compatibility, which should make it work with the usual rails gems.

http://sequel.jeremyevans.net/rdoc-plugins/classes/Sequel/Pl...

Sequel is my favourite of the tools I use.

I don't have experience with Sequel and rails 5 specifically. The thing is, models are really not very coupled to rails. We don't have to do anything special to use Sequel models - it has good support for Rails migrations and everything.

Regarding authentication, my company makes authorization and access control software, so authentication isn't something we just toss a plugin at.