Authentication Systems: DIY vs Managed

Wanted to understand the real difference between building your own backend versus using managed services. What do you gain? What do you lose?

Built identical Flutter apps with login/signup flows—one using a Spring Boot backend I wrote from scratch, one using Supabase. Both handle JWTs, secure storage, password validation, and all the security stuff that matters. Same features, different approaches.

Spring Boot version: Complete control, but you handle everything—token refresh, password hashing, email verification, session management. Supabase version: Fast to ship, but you're tied to their ecosystem. Trade-off: time-to-market vs flexibility. Answer depends on your constraints.