認証プロバイダーを選ぶ

When you add login, you face an early fork: write the auth system yourself, or use a provider that handles it for you. For most apps built by prompting, a provider is the safer, faster choice.

Auth is deceptively hard to get right. Providers have already solved password storage, email verification, social login, and security edge cases that take months to build alone.

A managed auth provider handles the heavy parts: storing credentials securely, sending verification and reset emails, issuing sessions or tokens, and often a ready-made login UI.

You connect to it with a small SDK and a few keys. Your job shifts from inventing security to wiring the provider into your app correctly.

A few names come up constantly. Supabase Auth and Firebase Auth bundle login with a database. Clerk and Auth0 focus purely on identity with polished UIs. NextAuth (Auth.js) is a popular self-hosted library for JavaScript frameworks.

Each fits different needs. Ask your assistant to weigh them against your specific stack rather than picking by popularity alone.

The best provider is usually the one that fits your existing tools. If you already use Supabase for your database, Supabase Auth saves a lot of glue code. If you're on Next.js, Auth.js and Clerk have first-class support.

Mismatched choices create friction: extra adapters, duplicated user records, and confusing docs. Lead your prompt with your current stack.

Modern providers offer more than email and password. Social login lets users sign in with Google, GitHub, or Apple. Magic links email a one-time login URL so there's no password at all.

These reduce signup friction but add setup steps, like registering OAuth apps. Decide which methods you actually need before wiring them in.

Providers are often free up to a point, then charge per monthly active user or per feature. A side project may stay free forever; a growing app can hit paid tiers fast.

Before committing, check the free limits and what happens when you exceed them. Switching providers later means migrating every user account, which is painful.

Hosted providers run on the vendor's servers; you trust them with user identity data. Self-hosted libraries keep everything in your own database and infrastructure.

Hosted is less work and more reliable. Self-hosted gives full control and avoids per-user fees, but you own the security and uptime. Weigh effort against control.

Every provider gives you keys: a public key for the browser and a secret key for the server. The secret must never appear in client code or get committed to git.

Store secrets in environment variables. A frequent vibe-coding mistake is pasting a secret key into a frontend file, exposing your entire auth system.

AI assistants know general patterns but can lag behind a provider's latest API. The safest workflow is to point your assistant at the current official docs and ask it to follow them.

This avoids deprecated methods and version mismatches that cause cryptic errors. Treat the docs as the source of truth, your assistant as the translator.

Lock-in is real. Some providers store users in your own database, making it easy to leave. Others keep identity data on their servers, so migrating means exporting accounts and forcing password resets.

You don't have to avoid lock-in entirely, but know the cost upfront. Ask whether your user data lives somewhere you can export.

Pull it together: pick the provider that matches your stack, covers the login methods you need, stays within budget, and stores data you can access.

Write the decision down in a short note so future prompts stay consistent. A clear choice now prevents half-finished, conflicting auth code later.

One key decision factor to lock in.

You learned that buying auth from a provider usually beats building it. You compared options like Supabase, Clerk, Firebase, and Auth.js, and saw how stack fit, login methods, pricing, and data ownership drive the choice.

You also learned to keep secret keys in environment variables and to point your assistant at the latest docs. With a provider chosen, you're ready to wire up sign-up and login.