Create Auth Skill

Guide for adding authentication to TypeScript/JavaScript applications using Better Auth.

For code examples and syntax, see better-auth.com/docs.

Decision Tree

Is this a new/empty project?
├─ YES → New project setup
│   1. Identify framework
│   2. Choose database
│   3. Install better-auth
│   4. Create auth.ts + auth-client.ts
│   5. Set up route handler
│   6. Run CLI migrate/generate
│   7. Add features via plugins
│
└─ NO → Does project have existing auth?
    ├─ YES → Migration/enhancement
    │   • Audit current auth for gaps
    │   • Plan incremental migration
    │   • See migration guides in docs
    │
    └─ NO → Add auth to existing project
        1. Analyze project structure
        2. Install better-auth
        3. Create auth config
        4. Add route handler
        5. Run schema migrations
        6. Integrate into existing pages

Installation

Core: npm install better-auth

Scoped packages (as needed):

Environment Variables

BETTER_AUTH_SECRET=<32+ chars, generate with: openssl rand -base64 32>
BETTER_AUTH_URL=http://localhost:3000
DATABASE_URL=<your database connection string>

Add OAuth secrets as needed: GITHUB_CLIENT_ID, GITHUB_CLIENT_SECRET, GOOGLE_CLIENT_ID, etc.

Server Config (auth.ts)

Location: lib/auth.ts or src/lib/auth.ts

Minimal config needs:

• database - Connection or adapter
• emailAndPassword: { enabled: true } - For email/password auth

Standard config adds:

• socialProviders - OAuth providers (google, github, etc.)
• emailVerification.sendVerificationEmail - Email verification handler
• emailAndPassword.sendResetPassword - Password reset handler

Full config adds:

• plugins - Array of feature plugins
• session - Expiry, cookie cache settings
• account.accountLinking - Multi-provider linking
• rateLimit - Rate limiting config

Export types: export type Session = typeof auth.$Infer.Session

Client Config (auth-client.ts)

Import by framework:

Client plugins go in createAuthClient({ plugins: [...] }).

Common exports: signIn, signUp, signOut, useSession, getSession

Route Handler Setup

Next.js Server Components: Add nextCookies() plugin to auth config.

Database Migrations

Re-run after adding plugins.

Database Adapters

Common Plugins

Plugin pattern: Server plugin + client plugin + run migrations.

Auth UI Implementation

Sign in flow:

1. signIn.email({ email, password }) or signIn.social({ provider, callbackURL })
2. Handle error in response
3. Redirect on success

Session check (client): useSession() hook returns { data: session, isPending }

Session check (server): auth.api.getSession({ headers: await headers() })

Protected routes: Check session, redirect to /sign-in if null.

Security Checklist

• BETTER_AUTH_SECRET set (32+ chars)
• advanced.useSecureCookies: true in production
• trustedOrigins configured
• Rate limits enabled
• Email verification enabled
• Password reset implemented
• 2FA for sensitive apps
• CSRF protection NOT disabled
• account.accountLinking reviewed

Troubleshooting

Resources

• Docs
• Examples
• Plugins
• CLI
• Migration Guides