Open-source Auth Platform
"Stack Auth is a managed user authentication solution. It is developer-friendly and fully open-source (licensed under MIT and AGPL).
Stack Auth gets you started in just five minutes, after which you'll be ready to use all of its features as you grow your project. Our managed service is completely optional and you can export your user data and self-host, for free, at any time.
We support Next.js, React, and JavaScript frontends, along with any backend that can use our REST API."