Redirect legacy document URLs after authentication without prerendering aliases

apps/docs/src/proxy.ts

@@ -1,5 +1,10 @@
 import { NextResponse, type NextRequest } from "next/server";
 import { authConfig, SESSION_COOKIE, validSession } from "./lib/auth";
+import catalog from "../../../content/catalog.json";
+
+const legacyRoutes = new Map(Object.entries(catalog.documents).map(([source, metadata]) => [
+  `/docs/${source}`, `/docs/${metadata.slug}`,
+]));
 
 export function proxy(request: NextRequest) {
   const path = request.nextUrl.pathname;
@@ -49,6 +54,13 @@ export function proxy(request: NextRequest) {
         );
       }
     }
+    // Keep legacy URLs behind authentication and out of static generation.
+    const destination = legacyRoutes.get(path);
+    if (destination && ["GET", "HEAD"].includes(request.method)) {
+      const target = request.nextUrl.clone();
+      target.pathname = destination;
+      return NextResponse.redirect(target, { status: 308, headers });
+    }
     return NextResponse.next({ headers });
   }
   if (path.startsWith("/api/") || !["GET", "HEAD"].includes(request.method)) {