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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Phase 1: Planning (REQUIRED before implementation)

Before writing any code, gather requirements by scanning the project and asking the user structured questions. This ensures the implementation matches their needs.

Step 1: Scan the project

Analyze the codebase to auto-detect:

• Framework — Look for next.config, svelte.config, nuxt.config, astro.config, vite.config, or Express/Hono entry files.
• Database/ORM — Look for prisma/schema.prisma, drizzle.config, package.json deps (pg, mysql2, better-sqlite3, mongoose, mongodb).
• Existing auth — Look for existing auth libraries (next-auth, lucia, clerk, supabase/auth, firebase/auth) in package.json or imports.
• Package manager — Check for pnpm-lock.yaml, yarn.lock, bun.lockb, or package-lock.json.

Use what you find to pre-fill defaults and skip questions you can already answer.

Step 2: Ask planning questions

Use the AskQuestion tool to ask the user all applicable questions in a single call. Skip any question you already have a confident answer for from the scan. Group them under a title like "Auth Setup Planning".

Questions to ask:

• Project type (skip if detected)

- Prompt: "What type of project is this?"

- Options: New project from scratch | Adding auth to existing project | Migrating from another auth library

• Framework (skip if detected)

- Prompt: "Which framework are you using?"

- Options: Next.js (App Router) | Next.js (Pages Router) | SvelteKit | Nuxt | Astro | Express | Hono | SolidStart | Other

• Database & ORM (skip if detected)

- Prompt: "Which database setup will you use?"

- Options: PostgreSQL (Prisma) | PostgreSQL (Drizzle) | PostgreSQL (pg driver) | MySQL (Prisma) | MySQL (Drizzle) | MySQL (mysql2 driver) | SQLite (Prisma) | SQLite (Drizzle) | SQLite (better-sqlite3 driver) | MongoDB (Mongoose) | MongoDB (native driver)

• Authentication methods (always ask, allow multiple)

- Prompt: "Which sign-in methods do you need?"

- Options: Email & password | Social OAuth (Google, GitHub, etc.) | Magic link (passwordless email) | Passkey (WebAuthn) | Phone number

- allow_multiple: true

• Social providers (only if they selected Social OAuth above — ask in a follow-up call)

- Prompt: "Which social providers do you need?"

- Options: Google | GitHub | Apple | Microsoft | Discord | Twitter/X

- allow_multiple: true

• Email verification (only if Email & password was selected above — ask in a follow-up call)

- Prompt: "Do you want to require email verification?"

- Options: Yes | No

• Email provider (only if email verification is Yes, or if Password reset is selected in features — ask in a follow-up call)

- Prompt: "How do you want to send emails?"

- Options: Resend | Mock it for now (console.log)

• Features & plugins (always ask, allow multiple)

- Prompt: "Which additional features do you need?"

- Options: Two-factor authentication (2FA) | Organizations / teams | Admin dashboard | API bearer tokens | Password reset | None of these

- allow_multiple: true

• Auth pages (always ask, allow multiple — pre-select based on earlier answers)

- Prompt: "Which auth pages do you need?"

- Options vary based on previous answers:

- Always available: Sign in | Sign up

- If Email & password selected: Forgot password | Reset password

- If email verification enabled: Email verification

- allow_multiple: true

• Auth UI style (always ask)

- Prompt: "What style do you want for the auth pages? Pick one or describe your own."

- Options: Minimal & clean | Centered card with background | Split layout (form + hero image) | Floating / glassmorphism | Other (I'll describe)

Step 3: Summarize the plan

After collecting answers, present a concise implementation plan as a markdown checklist. Example:

## Auth Implementation Plan

Framework: Next.js (App Router)
Database: PostgreSQL via Prisma
Auth methods: Email/password, Google OAuth, GitHub OAuth
Plugins: 2FA, Organizations, Email verification
UI: Custom forms

Steps
Install better-auth and @better-auth/cli
Create lib/auth.ts with server config
Create lib/auth-client.ts with React client
Set up route handler at app/api/auth/[...all]/route.ts
Configure Prisma adapter and generate schema
Add Google & GitHub OAuth providers
Enable twoFactor and organization plugins
Set up email verification handler
Run migrations
Create sign-in / sign-up pages

Ask the user to confirm the plan before proceeding to Phase 2.

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Phase 2: Implementation

Only proceed here after the user confirms the plan from Phase 1.

Follow the decision tree below, guided by the answers collected above.

Is this a new/empty project?
├─ YES → New project setup
│   1. Install better-auth (+ scoped packages per plan)
│   2. Create auth.ts with all planned config
│   3. Create auth-client.ts with framework client
│   4. Set up route handler
│   5. Set up environment variables
│   6. Run CLI migrate/generate
│   7. Add plugins from plan
│   8. Create auth UI pages
│
├─ MIGRATING → Migration from existing auth
│   1. Audit current auth for gaps
│   2. Plan incremental migration
│   3. Install better-auth alongside existing auth
│   4. Migrate routes, then session logic, then UI
│   5. Remove old auth library
│   6. See migration guides in docs
│
└─ ADDING → Add auth to existing project
    1. Analyze project structure
    2. Install better-auth
    3. Create auth config matching plan
    4. Add route handler
    5. Run schema migrations
    6. Integrate into existing pages
    7. Add planned plugins and features

At the end of implementation, guide users thoroughly on remaining next steps (e.g., setting up OAuth app credentials, deploying env vars, testing flows).

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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:

• signIn.email({ email, password }) or signIn.social({ provider, callbackURL })
• Handle error in response
• 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