feat(authz): add request middleware, can(), and guardPermission

Installs a per-request authz resolver via authzMiddleware and exposes
can()/decideFor()/guardPermission()/filterCan() as free functions (not
Context members, so @wrnexus/core stays free of an authz dependency).
All four route through resolver.decide(), never permissionsFor(), so
resource-scoped policy denials can't be bypassed via the coarse
permission set. Per-request results are memoised keyed on (permission,
resource) to avoid re-hitting the store within a request without
leaking one resource's verdict onto another.

packages/authz/test/middleware.test.ts

@@ -0,0 +1,142 @@
+import { describe, expect, test } from "bun:test";
+import type { Context } from "@wrnexus/core";
+import { defineAuthz } from "../src/registry.ts";
+import { mergeCatalogs } from "../src/catalog.ts";
+import { memoryPermissionStore } from "../src/store.ts";
+import { authzMiddleware, can, filterCan, guardPermission } from "../src/middleware.ts";
+
+const catalog = mergeCatalogs([
+  {
+    source: "t.ts",
+    module: defineAuthz({
+      permissions: { "post:read": { public: true }, "post:write": {}, "post:delete": {} },
+      roles: { editor: ["post:write"] },
+      policies: {
+        ownsPost: async (s: { id?: string }, r?: { authorId?: string }) =>
+          r?.authorId === s?.id ? { allowed: true } : { allowed: false, reason: "not owner" },
+      },
+      bindings: { "post:delete": ["ownsPost"] },
+    }),
+  },
+]);
+
+/** Minimal Context stand-in; the middleware only touches user, tenant, locals. */
+function makeCtx(user: unknown, tenantId?: string): Context {
+  return {
+    user,
+    tenant: tenantId ? { id: tenantId } : undefined,
+    locals: {},
+    url: new URL("http://localhost/x"),
+    req: new Request("http://localhost/x"),
+  } as unknown as Context;
+}
+
+const withMiddleware = async (ctx: Context, store = memoryPermissionStore()) => {
+  await authzMiddleware({ catalog, store, strict: false })(ctx, async () => new Response("ok"));
+  return store;
+};
+
+describe("authzMiddleware + can", () => {
+  test("can() resolves through the middleware-installed resolver", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    const store = memoryPermissionStore();
+    await store.assignRole("u1", "editor");
+    await withMiddleware(ctx, store);
+    expect(await can(ctx, "post:write")).toBe(true);
+    expect(await can(ctx, "post:delete", { authorId: "u1" })).toBe(false);
+  });
+
+  test("can() throws a clear setup error without the middleware", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    await expect(can(ctx, "post:read")).rejects.toThrow(/authzMiddleware/);
+  });
+
+  test("results are memoised per request", async () => {
+    const inner = memoryPermissionStore();
+    let reads = 0;
+    const counting = {
+      ...inner,
+      assignmentsFor: (id: string, scope?: { tenantId?: string }) => {
+        reads++;
+        return inner.assignmentsFor(id, scope);
+      },
+    };
+    const ctx = makeCtx({ id: "u1" });
+    await authzMiddleware({ catalog, store: counting, strict: false })(
+      ctx,
+      async () => new Response("ok"),
+    );
+    await can(ctx, "post:write");
+    await can(ctx, "post:write");
+    expect(reads).toBe(1);
+  });
+
+  test("memoisation keys on the resource, not just the permission", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    const store = memoryPermissionStore();
+    await store.grant("u1", "post:delete", "allow");
+    await withMiddleware(ctx, store);
+    expect(await can(ctx, "post:delete", { authorId: "u1" })).toBe(true);
+    expect(await can(ctx, "post:delete", { authorId: "other" })).toBe(false);
+  });
+
+  test("the tenant on the context becomes the scope", async () => {
+    const ctx = makeCtx({ id: "u1" }, "t1");
+    const store = memoryPermissionStore();
+    await store.assignRole("u1", "editor", { tenantId: "t1" });
+    await withMiddleware(ctx, store);
+    expect(await can(ctx, "post:write")).toBe(true);
+  });
+});
+
+describe("guardPermission", () => {
+  test("calls next when allowed", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    const store = memoryPermissionStore();
+    await store.assignRole("u1", "editor");
+    await withMiddleware(ctx, store);
+    const res = await guardPermission("post:write")(ctx, async () => new Response("passed"));
+    expect(await res.text()).toBe("passed");
+  });
+
+  test("returns 403 without leaking the reason by default", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    await withMiddleware(ctx);
+    const res = await guardPermission("post:write")(ctx, async () => new Response("passed"));
+    expect(res.status).toBe(403);
+    const body = (await res.json()) as Record<string, unknown>;
+    expect(body).toEqual({ ok: false, error: "Forbidden" });
+  });
+
+  test("exposeReason opts into diagnostics", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    await withMiddleware(ctx);
+    const res = await guardPermission("post:write", { exposeReason: true })(
+      ctx,
+      async () => new Response("passed"),
+    );
+    const body = (await res.json()) as Record<string, unknown>;
+    expect(body.reason).toBe("Missing permission");
+  });
+
+  test("getResource feeds the bound policy", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    const store = memoryPermissionStore();
+    await store.grant("u1", "post:delete", "allow");
+    await withMiddleware(ctx, store);
+    const guard = guardPermission("post:delete", { getResource: () => ({ authorId: "u1" }) });
+    const res = await guard(ctx, async () => new Response("passed"));
+    expect(await res.text()).toBe("passed");
+  });
+});
+
+describe("filterCan", () => {
+  test("keeps only the items the subject may act on", async () => {
+    const ctx = makeCtx({ id: "u1" });
+    const store = memoryPermissionStore();
+    await store.grant("u1", "post:delete", "allow");
+    await withMiddleware(ctx, store);
+    const posts = [{ authorId: "u1" }, { authorId: "other" }, { authorId: "u1" }];
+    expect(await filterCan(ctx, "post:delete", posts)).toHaveLength(2);
+  });
+});