What's the story around extensibility? I feel like it starts to get murky when the boundaries of data ownership are unclear. What if I have some bespoke user-level data that doesn't make sense for your system to store, but is massively important to my business (this feels to be the case for most products I build).

Can customers extend your UI components? Do they store that data with you? One of the nice parts about authentication only is that it's relatively well-defined and not a place where customers frequently have variable needs (outside of just data sources to auth against).

Cool idea either way though, and I like seeing more innovation in the space.