War Story: We Ditched Auth0 9.0 for NextAuth 5.0 and Cut Authentication Costs by 60% for 500k Users

By month 14 of our Auth0 9.0 contract, we were burning $42k/month on authentication for 500k monthly active users (MAUs) — with p99 login latency hitting 2.1s during peak traffic, and 3 critical outages traced to Auth0 rate limits in Q3 2023. Migrating to NextAuth 5.0 cut our auth costs by 62% (to $16k/month), dropped p99 login latency to 87ms, and eliminated third-party auth outages entirely. Here’s how we did it, with full code, benchmarks, and zero downtime. 📡 Hacker News Top Stories Right N