create-auth-skill

---
name: create-auth-skill
description: Scaffold and implement authentication in TypeScript/JavaScript apps using Better Auth. Detect frameworks, configure database adapters, set up route handlers, add OAuth providers, and create auth UI pages. Use when users want to add login, sign-up, or authentication to a new or existing project with Better Auth.
metadata:
  author: epicenter
  version: '1.0'
---

# Create Auth Skill

## Reference Repositories

- [Better Auth](https://github.com/better-auth/better-auth) — TypeScript authentication framework with plugins

## Upstream Grounding

When Better Auth API signatures, framework handlers, adapter setup, generated schema, plugin options, session behavior, or security defaults affect correctness, ask DeepWiki a narrow question against `better-auth/better-auth` before relying on memory. Use it to orient, then verify decisive details against local installed types, source, or official docs before changing code.

Skip DeepWiki for stable planning steps and repo-local conventions already documented below.

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

**For code examples and syntax, see [better-auth.com/docs](https://better-auth.com/docs).**

## When to Apply This Skill

Use this pattern when you need to:

- Add Better Auth login/sign-up to a new or existing TypeScript/JavaScript app.
- Plan auth implementation by detecting framework, DB, and existing auth stack.
- Configure `auth.ts`, client setup, route handlers, and migrations.
- Add OAuth providers, plugins, and auth pages based on project requirements.
- Migrate incrementally from another auth library to Better Auth.

---

## 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:**

1. **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

2. **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

3. **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)

4. **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`

5. **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`

6. **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

7. **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)

8. **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`

9. **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`

10. **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
1. Install `better-auth` and `@better-auth/cli`
2. Create `lib/auth.ts` with server config
3. Create `lib/auth-client.ts` with React client
4. Set up route handler at `app/api/auth/[...all]/route.ts`
5. Configure Prisma adapter and generate schema
6. Add Google & GitHub OAuth providers
7. Enable `twoFactor` and `organization` plugins
8. Set up email verification handler
9. Run migrations
10. Create sign-in / sign-up pages
```

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

---

## 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).

---

## 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 |

---

## Environment Variables

```env
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:**
| 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`

---

## 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.

---

## 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.**

---

## 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` |

---

## 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.

---

## 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

| 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 |

---

## Resources

- [Docs](https://better-auth.com/docs)
- [Examples](https://github.com/better-auth/examples)
- [Plugins](https://better-auth.com/docs/concepts/plugins)
- [CLI](https://better-auth.com/docs/concepts/cli)
- [Migration Guides](https://better-auth.com/docs/guides)