I'd advocate that the right "simple" solution is a platform/framework specific auth solution (as I wrote here: https://news.ycombinator.com/item?id=38872704 ).
Those handle a lot of the simple use cases and some of the complex ones. They have the virtue of being well-tested and integrated with your development platform. You can deploy in one step and maintain one database. Which is great till it isn't.
What platform libraries like Devise, etc, don't offer is user data denormalization and isolation, which is useful when you have 2 or more applications with users. Then you want to look at auth servers (self-hosted or SaaS).
But you want the auth server experience to be as simple as possible, which is what we're working towards.
My two cents.
My thoughts exactly. I want a simple auth solution that doesn’t push me towards a full batteries-included platform like Firebase and Amplify, nor a highly-configurable/complex “you can do everything auth!” platform. It’s ok if it’s a little opinionated, as long as it serves my use case of “adding logins and SSO to my website” up to 90% of the problem instead of 50% like what’s out there now.
It seems like an underserved market.
This is pretty much exactly what we built at WorkOS. (I work there.)
Check it out: https://workos.com/
And our Show HN launch a few years ago: https://news.ycombinator.com/item?id=22607402
This sounds like there should be two solutions, one for the simpler case and one for the complex case, rather than trying to make one solution work for all use cases.