NextAuth Secret Generator

Common mistakes

⚠Using the same AUTH_SECRET in development and production

⚠Committing AUTH_SECRET to git — add .env.local to .gitignore

⚠Doing a rolling deploy when rotating the secret — all instances must get the new secret simultaneously

⚠Using a short or password-derived secret — minimum 32 bytes of true randomness required

AUTH_SECRET vs NEXTAUTH_SECRET

Auth.js v5 renamed the environment variable from NEXTAUTH_SECRET to AUTH_SECRET. If you are starting a new project today, use AUTH_SECRET. If you are on next-auth@4, use NEXTAUTH_SECRET. Both require the same thing: a random, high-entropy string kept secret on the server.

What does the secret actually do?

Auth.js uses the secret to sign and verify JWTs (session tokens), to encrypt cookies, and to derive CSRF tokens. The minimum safe length is 32 bytes (256 bits), encoded as base64. This matches what openssl rand -base64 32 produces and what npx auth secret generates.

How to add it to your project

Copy the generated value and paste it into your .env.local:
```
AUTH_SECRET=<paste here>
```
Add it to your hosting provider (Vercel, Railway, Fly.io) under production environment variables — never check it into git.
Add the key with a blank value to .env.example:
```
AUTH_SECRET=
```

Rotating the secret

Rotate if you suspect the secret was exposed. When you rotate, all existing sessions immediately invalidate — users are logged out. Auth.js v5 supports an array value for graceful rotation (new secret first, old secret still accepted). Deploy atomically — never mix old and new secrets across instances.

Frequently asked questions

AUTH_SECRET vs NEXTAUTH_SECRET — which do I use?

Auth.js v5 (the successor to NextAuth v4) renamed the variable from NEXTAUTH_SECRET to AUTH_SECRET. If you are starting a new project today with next-auth@5 or auth@latest, use AUTH_SECRET. If you are on next-auth@4, use NEXTAUTH_SECRET. Both require the same thing: a random, high-entropy string kept secret on the server.

What happens if AUTH_SECRET leaks?

An attacker with your secret can forge session tokens and impersonate any user in your application. Rotate immediately: generate a new secret, update it in all environments (preview, staging, production), and redeploy atomically. A rolling deploy with mixed secrets breaks auth for users mid-session.

Is this the same as running openssl rand -base64 32?

Yes — functionally identical. This tool uses crypto.getRandomValues (the browser's CSPRNG) to generate 32 bytes and encodes them as standard base64, exactly matching openssl rand -base64 32 output. You can use either method.

Does Auth.js support graceful secret rotation?

Yes. Auth.js v5 supports an array value for AUTH_SECRET — the first entry is used for signing new tokens, and remaining entries are accepted for verification. This allows a zero-downtime rotation: add the new secret first, deploy, then remove the old secret in a follow-up deploy.

What it does

Privacy

When to use this tool