Implement Authentication Service in Rails

Hello,

I'm currently looking for options to create some form of authentication service based on Rails.

I've got several microservices like app1.site.com app2.site.com and app3.site.com and I would like to have something like auth.site.com so users only have to create their accounts once and use them across sites...

I don't think there's a Devise option that can be used. My research points to Okta or Auth0 which are now, very recently, the same apparently.

What's the right way to implement this? whether is through an external service provider or some other form of custom build application with the help of already existing gems.