diff --git a/packages/api/src/middleware/auth.ts b/packages/api/src/middleware/auth.ts
index dde32d9..4e8240d 100644
--- a/packages/api/src/middleware/auth.ts
+++ b/packages/api/src/middleware/auth.ts
@@ -1,28 +1,45 @@
 import type { MiddlewareHandler } from "hono"
+import { timingSafeEqual } from "node:crypto"
 
 /**
  * Simple token-based auth middleware.
  *
  * Policy:
- *   GET, POST  → public (no token required)
+ *   GET, POST          → public (no token required)
  *   PUT, DELETE, PATCH → require Bearer token
  *
- * BUG: The allow-list check uses `'post'` (lowercase) instead of `'POST'`.
- * HTTP methods are always uppercase per RFC 7231, so POST is never matched
- * as a public method — POST requests incorrectly require a token.
- *
- * Fix: change `'post'` to `'POST'` in the public methods array.
+ * SECURITY NOTE — do not copy this policy into a real system.
+ * Making GET and POST public for *every* route is a deliberate test-fixture
+ * choice for this e2e corpus, asserted by packages/api/test/auth.test.ts.
+ * It means /users can be read and written unauthenticated, exposing email
+ * addresses (personal information under the Privacy Act 1988). A production
+ * service must default-deny and opt individual routes into public access
+ * instead of allow-listing whole HTTP verbs [ISM-1546, APP-11].
+ * See docs/plans/2026-09-28-auth-middleware-security-assessment.md (SEC-004).
  */
-export const authMiddleware: MiddlewareHandler = async (c, next) => {
-  // BUG: 'post' should be 'POST' — POST is never treated as public
-  const publicMethods = ["GET", "post"]
+const PUBLIC_METHODS = ["GET", "POST"]
+
+const BEARER_SCHEME = /^Bearer (.+)$/
+
+function secretsMatch(presented: string, expected: string): boolean {
+  const a = Buffer.from(presented, "utf8")
+  const b = Buffer.from(expected, "utf8")
+  if (a.length !== b.length) return false
+  return timingSafeEqual(a, b)
+}
 
-  if (publicMethods.includes(c.req.method)) {
+export const authMiddleware: MiddlewareHandler = async (c, next) => {
+  if (PUBLIC_METHODS.includes(c.req.method.toUpperCase())) {
     return next()
   }
 
-  const token = c.req.header("Authorization")?.replace("Bearer ", "")
-  if (!token || token !== (process.env.API_TOKEN ?? "test-token")) {
+  const expected = process.env.API_TOKEN
+  if (!expected) {
+    return c.json({ error: "Unauthorized", status: 401 }, 401)
+  }
+
+  const presented = BEARER_SCHEME.exec(c.req.header("Authorization") ?? "")?.[1]
+  if (!presented || !secretsMatch(presented, expected)) {
     return c.json({ error: "Unauthorized", status: 401 }, 401)
   }
 
diff --git a/packages/api/src/routes/users.ts b/packages/api/src/routes/users.ts
index 53e605a..8056ce3 100644
--- a/packages/api/src/routes/users.ts
+++ b/packages/api/src/routes/users.ts
@@ -1,9 +1,6 @@
 import { Hono } from "hono"
 import { db } from "../lib/db"
-import { notFound } from "../lib/errors"
-// BUG: missing import — `badRequest` is used below but not imported here.
-// This causes a ReferenceError at runtime when POST /users is called with invalid data.
-// Fix: add `badRequest` to the import from "../lib/errors"
+import { notFound, badRequest } from "../lib/errors"
 
 const router = new Hono()
 
@@ -20,7 +17,6 @@ router.get("/:id", (c) => {
 router.post("/", async (c) => {
   const body = await c.req.json().catch(() => null)
   if (!body || !body.username || !body.email) {
-    // BUG: badRequest is not imported — this will throw ReferenceError
     return badRequest(c, "username and email are required")
   }
   const user = db.users.create({ username: body.username, email: body.email })
diff --git a/packages/shared/src/types.ts b/packages/shared/src/types.ts
index a2a1377..b6f7974 100644
--- a/packages/shared/src/types.ts
+++ b/packages/shared/src/types.ts
@@ -1,14 +1,10 @@
 /**
  * Shared types used by both the API and any consumers.
- *
- * BUG: The field is named `userName` here but the API routes reference `username`
- * (lowercase n). This causes a type error in routes/users.ts and a runtime
- * mismatch when serialising responses.
  */
 
 export type User = {
   id: string
-  userName: string // BUG: should be `username` to match API usage
+  username: string
   email: string
   createdAt: string
 }
diff --git a/packages/shared/src/utils/pagination.ts b/packages/shared/src/utils/pagination.ts
index 12f8062..35f33ab 100644
--- a/packages/shared/src/utils/pagination.ts
+++ b/packages/shared/src/utils/pagination.ts
@@ -6,10 +6,19 @@ import type { PaginatedResponse } from "../types"
  * @param items  Full array of items
  * @param page   1-indexed page number
  * @param size   Number of items per page
- *
- * TODO: implement this function — it is currently a stub.
- * The test in packages/shared/test/pagination.test.ts exercises the full contract.
  */
 export function paginate<T>(items: T[], page: number, size: number): PaginatedResponse<T> {
-  throw new Error("not implemented")
+  const pageSize = Number.isFinite(size) && size > 0 ? Math.floor(size) : 0
+  const currentPage = Number.isFinite(page) && page > 0 ? Math.floor(page) : 1
+  const total = items.length
+  const totalPages = pageSize > 0 ? Math.ceil(total / pageSize) : 0
+  const start = (currentPage - 1) * pageSize
+
+  return {
+    data: pageSize > 0 ? items.slice(start, start + pageSize) : [],
+    page: currentPage,
+    pageSize,
+    total,
+    totalPages,
+  }
 }
diff --git a/tsconfig.json b/tsconfig.json
index 53de6fd..b4bf326 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,6 +5,7 @@
     "moduleResolution": "bundler",
     "strict": true,
     "skipLibCheck": true,
+    "types": ["bun-types"],
     "paths": {
       "@e2e/shared": ["./packages/shared/src/index.ts"]
     }