add middleware (#685)

To resolve CORS error when calling the UserOpBuilder service endpoints

Author: KannuSingh

advanced/wallets/react-wallet-v2/src/pages/_middleware.ts

@@ -0,0 +1,36 @@
+import { NextResponse, NextRequest } from 'next/server'
+
+export function middleware(req: NextRequest) {
+  const res = NextResponse.next()
+
+  const origin = req.headers.get('origin')
+
+  if (process.env.NODE_ENV === 'production') {
+    // In production, allow all origins
+    res.headers.set('Access-Control-Allow-Origin', '*')
+  } else {
+    // In development, only allow localhost
+    const allowedOrigins = ['http://localhost:3000']
+    if (origin && allowedOrigins.includes(origin)) {
+      res.headers.set('Access-Control-Allow-Origin', origin)
+    }
+  }
+
+  // Common headers for both environments
+  res.headers.set('Access-Control-Allow-Methods', 'GET, POST, OPTIONS')
+  res.headers.set('Access-Control-Allow-Headers', 'Content-Type, Authorization')
+
+  // Handle preflight requests
+  if (req.method === 'OPTIONS') {
+    return new Response(null, {
+      status: 204,
+      headers: {
+        'Access-Control-Allow-Origin': process.env.NODE_ENV === 'production' ? '*' : (origin || ''),
+        'Access-Control-Allow-Methods': 'GET, POST, OPTIONS',
+        'Access-Control-Allow-Headers': 'Content-Type, Authorization'
+      }
+    })
+  }
+
+  return res
+}