nextjs-middleware

# Next.js Middleware Skill

Patterns for using Next.js middleware for request interception.

## Basic Middleware

### Simple Middleware

```typescript
// middleware.ts (in project root)
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

export function middleware(request: NextRequest) {
  // Clone the request headers
  const requestHeaders = new Headers(request.headers)
  requestHeaders.set('x-custom-header', 'custom-value')

  // Return response with modified headers
  return NextResponse.next({
    request: {
      headers: requestHeaders,
    },
  })
}

// Configure which paths middleware runs on
export const config = {
  matcher: '/api/:path*',
}
```

### Route Matching

```typescript
export const config = {
  matcher: [
    // Match all paths except static files and images
    '/((?!_next/static|_next/image|favicon.ico).*)',

    // Match specific paths
    '/api/:path*',
    '/dashboard/:path*',

    // Match with regex
    '/blog/:slug*',
  ],
}
```

## Authentication

### Session Check

```typescript
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
import { getToken } from 'next-auth/jwt'

export async function middleware(request: NextRequest) {
  const token = await getToken({ req: request })

  if (!token) {
    const signInUrl = new URL('/auth/signin', request.url)
    signInUrl.searchParams.set('callbackUrl', request.url)
    return NextResponse.redirect(signInUrl)
  }

  return NextResponse.next()
}

export const config = {
  matcher: ['/dashboard/:path*', '/account/:path*'],
}
```

### JWT Verification

```typescript
import { jwtVerify } from 'jose'
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

const SECRET = new TextEncoder().encode(process.env.JWT_SECRET)

export async function middleware(request: NextRequest) {
  const token = request.cookies.get('token')?.value

  if (!token) {
    return NextResponse.redirect(new URL('/logi