Set Cache-Control on every rendered page, and record the CSRF token's unbinding

src/http/app.test.ts

@@ -284,6 +284,43 @@ test("every response carries the security headers; HSTS follows SECURE_COOKIES",
   assert.match(res.headers.get("strict-transport-security") ?? "", /max-age=\d+/);
 });
 
+test("Cache-Control: every host response is private, no-store; only the anonymous built-in landing may be shared-cached", async (t) => {
+  const NO_STORE = "private, no-store";
+  const csrf = (await fetch(base + "/")).headers.get("set-cookie")?.split(";")[0] ?? "";
+  assert.match(csrf, new RegExp(`^${CSRF_COOKIE}=`));
+
+  // A first visit mints a per-visitor cookie, so that response must not be shared.
+  assert.equal((await fetch(base + "/")).headers.get("cache-control"), NO_STORE);
+  // The same page for an anonymous visitor who already holds the cookie is identical for all of them.
+  assert.equal((await fetch(base + "/", { headers: { cookie: csrf } })).headers.get("cache-control"), "public, max-age=0, s-maxage=60");
+  assert.equal((await fetch(base + "/", { headers: { cookie: csrf }, method: "HEAD" })).headers.get("cache-control"), "public, max-age=0, s-maxage=60");
+  // Signed in, the same URL carries that user's menu and sign-out form.
+  assert.equal((await fetch(base + "/", { headers: { cookie: `${csrf}; ${session()}` } })).headers.get("cache-control"), NO_STORE);
+
+  assert.equal((await fetch(base + "/dashboard", { headers: { cookie: session() } })).headers.get("cache-control"), NO_STORE);
+  assert.equal((await fetch(base + "/dashboard", { redirect: "manual" })).headers.get("cache-control"), NO_STORE); // sign-in bounce
+  assert.equal((await fetch(base + "/nope", { headers: { cookie: csrf } })).headers.get("cache-control"), NO_STORE); // 404
+  // An asset is the same bytes for everyone; its caching is not this header's job.
+  assert.equal((await fetch(base + "/public/css/styles.css")).headers.get("cache-control"), null);
+
+  // A plugin's pages and JSON default to no-store too, and a route that is the same for everyone opts in itself.
+  const shared: Plugin = {
+    apiVersion: "1.0.0",
+    home: () => ({ html: "<p>plugin home</p>" }),
+    id: "demo",
+    routes: [
+      { handler: () => ({ html: "open" }), method: "GET", path: "/open", public: true },
+      { handler: () => ({ headers: { "Cache-Control": "public, max-age=600" }, html: "same" }), method: "GET", path: "/same", public: true },
+      { handler: () => ({ json: { ok: true } }), method: "GET", path: "/data", public: true },
+    ],
+  };
+  const url = await startApp(t, [shared]);
+  for (const path of ["/demo/open", "/demo/data", "/"]) {
+    assert.equal((await fetch(url + path, { headers: { cookie: csrf } })).headers.get("cache-control"), NO_STORE, path);
+  }
+  assert.equal((await fetch(url + "/demo/same")).headers.get("cache-control"), "public, max-age=600");
+});
+
 // Production caches compiled templates; rendering must stay correct across repeated requests.
 test("renders correctly with template caching enabled", async () => {
   const app = createApp({ cache: true });