docs: setting middleware at build time (#23480)

docs/2.guide/2.directory-structure/1.middleware.md

@@ -171,3 +171,31 @@ definePageMeta({
 Now, before navigation to that page can complete, the `auth` route middleware will be run.
 
 :link-example{to="/docs/examples/routing/middleware"}
+
+## Setting Middleware At Build Time
+
+Instead of using `definePageMeta` on each page, you can add named route middleware within the `pages:extend` hook.
+
+```ts [nuxt.config.ts]
+import type { NuxtPage } from 'nuxt/schema'
+
+export default defineNuxtConfig({
+  hooks: {
+    'pages:extend' (pages) {
+      function setMiddleware (pages: NuxtPage[]) {
+        for (const page of pages) {
+          if (/* some condition */ true) {
+            page.meta ||= {}
+            // Note that this will override any middleware set in `definePageMeta` in the page
+            page.meta.middleware = ['named']
+          }
+          if (page.children) {
+            setMiddleware(page.children)
+          }
+        }
+      }
+      setMiddleware(pages)
+    }
+  }
+})
+```