nextjs-authentication

## Quick Reference

| Auth.js Export | Purpose | Usage |
|----------------|---------|-------|
| `auth` | Get session (server) | `const session = await auth()` |
| `signIn` | Trigger sign in | `await signIn('github')` |
| `signOut` | Trigger sign out | `await signOut()` |
| `handlers` | API route handlers | `export const { GET, POST } = handlers` |

| Session Access | Location | Code |
|----------------|----------|------|
| Server Component | Server | `const session = await auth()` |
| Client Component | Client | `const { data: session } = useSession()` |
| Middleware | Edge | `req.auth` |
| Server Action | Server | `const session = await auth()` |

| Protection Pattern | Location | Method |
|--------------------|----------|--------|
| Route-level | `middleware.ts` | Check `req.auth` |
| Page-level | Server Component | `if (!session) redirect()` |
| Component-level | Client | `useSession()` + guard |
| Action-level | Server Action | `await auth()` check |

## When to Use This Skill

Use for **authentication and authorization**:
- Setting up NextAuth.js (Auth.js v5)
- Adding OAuth providers (GitHub, Google, etc.)
- Implementing credentials-based login
- Protecting routes with middleware
- Role-based access control

**Related skills:**
- For middleware patterns: see `nextjs-middleware`
- For Server Actions: see `nextjs-server-actions`
- For form handling: see `nextjs-server-actions`

---

# Next.js Authentication

## NextAuth.js (Auth.js)

### Installation and Setup

```bash
npm install next-auth@beta
```

```tsx
// auth.ts
import NextAuth from 'next-auth';
import GitHub from 'next-auth/providers/github';
import Google from 'next-auth/providers/google';
import Credentials from 'next-auth/providers/credentials';
import { PrismaAdapter } from '@auth/prisma-adapter';
import { prisma } from '@/lib/prisma';
import bcrypt from 'bcryptjs';

export const { handlers, signIn, signOut, auth } = NextAuth({
  adapter: PrismaAdapter(prisma),
  providers: [
    GitHub({
      clientI