Redirect legacy document URLs after authentication without prerendering aliases

apps/docs/src/pages/docs/[...slug].tsx

@@ -25,16 +25,14 @@ import { headingsFor } from "@/lib/navigation";
 
 type Props = { doc: Doc; docs: DocLink[] };
 export const getStaticPaths: GetStaticPaths = async () => ({
-  paths: (await listDocs()).flatMap(({ slug, sourceSlug }) => [...new Set([slug, sourceSlug])].map((value) => ({ params: { slug: value.split("/") } }))),
+  paths: (await listDocs()).map(({ slug }) => ({ params: { slug: slug.split("/") } })),
   fallback: false,
 });
 export const getStaticProps: GetStaticProps<Props> = async ({ params }) => {
   const slug = Array.isArray(params?.slug) ? params.slug.join("/") : params?.slug;
   if (typeof slug !== "string") return { notFound: true };
   const docs = await listDocs();
-  const match = docs.find((d) => d.slug === slug || d.sourceSlug === slug);
-  if (!match) return { notFound: true };
-  if (slug !== match.slug) return { redirect: { destination: `/docs/${match.slug}`, permanent: true } };
+  if (!docs.some((d) => d.slug === slug)) return { notFound: true };
   return { props: { doc: await readDoc(slug), docs } };
 };
 function textOf(value: ReactNode): string {

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)) {