fix: use Web Crypto API in middleware (Edge Runtime compat)

middleware.ts

@@ -1,11 +1,18 @@
 import { NextResponse } from 'next/server'
 import type { NextRequest } from 'next/server'
-import * as crypto from 'crypto'
 
-export function middleware(request: NextRequest) {
+async function hmacSha256(secret: string, message: string): Promise<string> {
+  const enc = new TextEncoder()
+  const key = await crypto.subtle.importKey(
+    'raw', enc.encode(secret), { name: 'HMAC', hash: 'SHA-256' }, false, ['sign']
+  )
+  const sig = await crypto.subtle.sign('HMAC', key, enc.encode(message))
+  return Array.from(new Uint8Array(sig)).map(b => b.toString(16).padStart(2, '0')).join('')
+}
+
+export async function middleware(request: NextRequest) {
   const { pathname } = request.nextUrl
 
-  // Allow auth API and static assets
   if (
     pathname.startsWith('/api/auth') ||
     pathname.startsWith('/_next') ||
@@ -18,15 +25,12 @@ export function middleware(request: NextRequest) {
   const token = request.cookies.get('auth_token')?.value
   const pin = process.env.APP_PIN || '1234'
   const secret = process.env.APP_SECRET || 'smart-home-default-secret-change-me'
-  const expectedToken = crypto.createHmac('sha256', secret).update(pin).digest('hex')
+  const expectedToken = await hmacSha256(secret, pin)
 
   if (token !== expectedToken) {
-    // For API routes, return 401
     if (pathname.startsWith('/api/')) {
       return NextResponse.json({ error: 'unauthorized' }, { status: 401 })
     }
-
-    // For page requests, rewrite to show login (handled client-side)
     const url = request.nextUrl.clone()
     url.searchParams.set('locked', '1')
     return NextResponse.rewrite(url)