I replaced Auth0 with an open source library in 30 minutes. Here is what broke.

A developer replaced Auth0 with the open source kavachOS library for a side project with about 12,000 monthly active users.

The main reason was cost: the Auth0 bill had climbed to $427 per month.

They chose kavachOS for Cloudflare Workers support and human-plus-agent authentication, then integrated email/password, magic links, Google, GitHub, sessions, and password reset into a Hono app.

The migration created six database tables and the basic server and frontend setup reportedly came together quickly, though some features still need more testing.

The case highlights how self-hosted auth can cut recurring costs, while trading a managed platform for a newer open source stack.