Create Auth Skill

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

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

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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

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Installation

Core: npm install better-auth

Scoped packages (as needed):

Package	Use case
@better-auth/passkey	WebAuthn/Passkey auth
@better-auth/sso	SAML/OIDC enterprise SSO
@better-auth/stripe	Stripe payments
@better-auth/scim	SCIM user provisioning
@better-auth/expo	React Native/Expo

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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.

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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

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Client Config (auth-client.ts)

Import by framework:

Framework	Import
React/Next.js	better-auth/react
Vue	better-auth/vue
Svelte	better-auth/svelte
Solid	better-auth/solid
Vanilla JS	better-auth/client

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

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

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Route Handler Setup

Framework	File	Handler
Next.js App Router	app/api/auth/[...all]/route.ts	toNextJsHandler(auth) → export { GET, POST }
Next.js Pages	pages/api/auth/[...all].ts	toNextJsHandler(auth) → default export
Express	Any file	app.all("/api/auth/*", toNodeHandler(auth))
SvelteKit	src/hooks.server.ts	svelteKitHandler(auth)
SolidStart	Route file	solidStartHandler(auth)
Hono	Route file	auth.handler(c.req.raw)

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

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Database Migrations

Adapter	Command
Built-in Kysely	npx @better-auth/cli@latest migrate (applies directly)
Prisma	npx @better-auth/cli@latest generate --output prisma/schema.prisma then npx prisma migrate dev
Drizzle	npx @better-auth/cli@latest generate --output src/db/auth-schema.ts then npx drizzle-kit push

Re-run after adding plugins.

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Database Adapters

Database	Setup
SQLite	Pass better-sqlite3 or bun:sqlite instance directly
PostgreSQL	Pass pg.Pool instance directly
MySQL	Pass mysql2 pool directly
Prisma	prismaAdapter(prisma, { provider: "postgresql" }) from better-auth/adapters/prisma
Drizzle	drizzleAdapter(db, { provider: "pg" }) from better-auth/adapters/drizzle
MongoDB	mongodbAdapter(db) from better-auth/adapters/mongodb

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Common Plugins

Plugin	Server Import	Client Import	Purpose
twoFactor	better-auth/plugins	twoFactorClient	2FA with TOTP/OTP
organization	better-auth/plugins	organizationClient	Teams/orgs
admin	better-auth/plugins	adminClient	User management
bearer	better-auth/plugins	-	API token auth
openAPI	better-auth/plugins	-	API docs
passkey	@better-auth/passkey	passkeyClient	WebAuthn
sso	@better-auth/sso	-	Enterprise SSO

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

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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.

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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

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Troubleshooting

Issue	Fix
"Secret not set"	Add BETTER_AUTH_SECRET env var
"Invalid Origin"	Add domain to trustedOrigins
Cookies not setting	Check baseURL matches domain; enable secure cookies in prod
OAuth callback errors	Verify redirect URIs in provider dashboard
Type errors after adding plugin	Re-run CLI generate/migrate

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Resources

• Docs
• Examples
• Plugins
• CLI
• Migration Guides