Gate a route or nav node on a session, not only a permission

src/auth/gate.test.ts

@@ -0,0 +1,28 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import type { User } from "../http/context.ts";
+import { allows, gatesSet } from "./gate.ts";
+
+const holder: User = { email: "holder@example.test", id: "01a06091-ba9f-765f-abf4-b5144c314bc7", permissions: ["x:read"] };
+const stranger: User = { email: "stranger@example.test", id: "01a06091-baa3-7b4d-810a-c9ee7e559d98", permissions: [] };
+
+test("allows: ungated and public are open to anyone; session needs a user; permission needs the token", () => {
+  assert.equal(allows({}, null), true);
+  assert.equal(allows({ public: true }, null), true);
+
+  assert.equal(allows({ session: true }, null), false);
+  assert.equal(allows({ session: true }, stranger), true); // signed in is the whole gate — no grant
+
+  assert.equal(allows({ permission: "x:read" }, null), false);
+  assert.equal(allows({ permission: "x:read" }, stranger), false);
+  assert.equal(allows({ permission: "x:read" }, holder), true);
+});
+
+test("gatesSet names the gates a declaration sets, so discovery can refuse more than one", () => {
+  assert.deepEqual(gatesSet({}), []);
+  assert.deepEqual(gatesSet({ session: true }), ["session"]);
+  assert.deepEqual(gatesSet({ permission: "x:read", public: true }), ["public", "permission"]);
+  assert.deepEqual(gatesSet({ permission: "x:read", public: true, session: true }), ["public", "session", "permission"]);
+  // `false` is not a gate — only a set one counts, so { session: false } is an ungated route.
+  assert.deepEqual(gatesSet({ public: false, session: false }), []);
+});

src/auth/gate.ts

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+// The coarse gate a route or nav node declares. One home for the rule, so the router and the menu
+// can never disagree about what a visitor may reach.
+import type { User } from "../http/context.ts";
+
+// Widest first: whoever passes an earlier gate passes it without holding anything.
+const GATES = ["public", "session", "permission"] as const;
+
+export interface Gate {
+  permission?: string | undefined; // the Keto Permission the caller must hold
+  public?: boolean | undefined; // anyone, signed in or not
+  session?: boolean | undefined; // any signed-in user, no grant needed
+}
+
+export function allows(gate: Gate, user: User | null): boolean {
+  if (gate.public === true) return true;
+  if (gate.session === true) return user !== null;
+  return gate.permission == null || (user?.permissions.includes(gate.permission) ?? false);
+}
+
+// Which gates a declaration sets — discovery refuses more than one, since they contradict.
+export function gatesSet(gate: Gate | null | undefined): string[] {
+  if (gate == null) return [];
+  return GATES.filter((name) => (name === "permission" ? gate.permission != null : gate[name] === true));
+}