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antigravity-claudekit/skills/ck-better-auth/SKILL.md
2026-02-16 14:02:42 +09:00

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---
name: ck-better-auth
description: >
Implements authentication and authorization using Better Auth library patterns.
Activate when user says 'add authentication', 'implement login', 'set up auth',
'user sessions', 'OAuth integration', or 'role-based access control'.
Accepts framework context (Next.js, Express, etc.) and provider requirements.
---
## Overview
Scaffolds and implements authentication flows using Better Auth (better-auth.com), covering session management, OAuth providers, email/password auth, and RBAC patterns.
## When to Use
- Setting up authentication from scratch in a web application
- Adding OAuth providers (GitHub, Google, Discord, etc.)
- Implementing session-based or JWT authentication
- Adding role-based or permission-based access control
- Securing API routes and server-side pages
## Don't Use When
- Project already has a working auth system and only needs minor fixes
- Building a purely public API with no user accounts
- Using a managed auth service like Clerk or Auth0 (those have their own SDKs)
- Mobile-only app requiring native auth flows
## Steps / Instructions
### 1. Install Better Auth
```bash
npm install better-auth
```
### 2. Configure Auth Instance
```typescript
// lib/auth.ts
import { betterAuth } from 'better-auth';
import { prismaAdapter } from 'better-auth/adapters/prisma';
import { prisma } from './prisma';
export const auth = betterAuth({
database: prismaAdapter(prisma, { provider: 'postgresql' }),
emailAndPassword: { enabled: true },
socialProviders: {
github: {
clientId: process.env.GITHUB_CLIENT_ID!,
clientSecret: process.env.GITHUB_CLIENT_SECRET!,
},
google: {
clientId: process.env.GOOGLE_CLIENT_ID!,
clientSecret: process.env.GOOGLE_CLIENT_SECRET!,
},
},
session: {
expiresIn: 60 * 60 * 24 * 7, // 7 days
updateAge: 60 * 60 * 24, // refresh if older than 1 day
},
});
```
### 3. Set Up API Route (Next.js)
```typescript
// app/api/auth/[...all]/route.ts
import { auth } from '@/lib/auth';
import { toNextJsHandler } from 'better-auth/next-js';
export const { GET, POST } = toNextJsHandler(auth);
```
### 4. Create Auth Client
```typescript
// lib/auth-client.ts
import { createAuthClient } from 'better-auth/react';
export const authClient = createAuthClient({
baseURL: process.env.NEXT_PUBLIC_APP_URL,
});
export const { signIn, signOut, signUp, useSession } = authClient;
```
### 5. Protect Routes (Next.js Middleware)
```typescript
// middleware.ts
import { auth } from '@/lib/auth';
import { NextRequest, NextResponse } from 'next/server';
export async function middleware(request: NextRequest) {
const session = await auth.api.getSession({
headers: request.headers,
});
if (!session && request.nextUrl.pathname.startsWith('/dashboard')) {
return NextResponse.redirect(new URL('/login', request.url));
}
return NextResponse.next();
}
export const config = {
matcher: ['/dashboard/:path*', '/settings/:path*'],
};
```
### 6. Add RBAC (Optional)
```typescript
import { betterAuth } from 'better-auth';
import { rbac } from 'better-auth/plugins';
export const auth = betterAuth({
// ...base config
plugins: [
rbac({
roles: {
admin: { permissions: ['read', 'write', 'delete'] },
user: { permissions: ['read'] },
},
}),
],
});
```
### 7. Database Schema Migration
Run Better Auth CLI to generate schema:
```bash
npx better-auth generate
npx prisma migrate dev --name add-auth-tables
```
### 8. Environment Variables Required
```bash
# .env (never commit this file)
BETTER_AUTH_SECRET=<generate with: openssl rand -base64 32>
BETTER_AUTH_URL=http://localhost:3000
GITHUB_CLIENT_ID=...
GITHUB_CLIENT_SECRET=...
GOOGLE_CLIENT_ID=...
GOOGLE_CLIENT_SECRET=...
```
## Notes
- Always generate `BETTER_AUTH_SECRET` with a cryptographically secure method
- Never expose client secrets in frontend code or version control
- Use HTTPS in production — sessions over HTTP are insecure
- Test OAuth flows with provider sandbox/test apps before production