fix(security): replace unvalidated user-role cookie with JWT verifica…

src/lib/auth/jwt.ts

@@ -0,0 +1,79 @@
+import { UserRole } from '@/types/api';
+
+interface JWTPayload {
+  sub: string;
+  role: UserRole;
+  email?: string;
+  iat?: number;
+  exp?: number;
+}
+
+/**
+ * Verifies a JWT token and returns its payload.
+ * Uses the Web Crypto API (Edge-compatible, works in Next.js middleware).
+ */
+export async function verifyToken(token: string | undefined | null): Promise<JWTPayload | null> {
+  if (!token) return null;
+
+  try {
+    const secret = process.env.JWT_SECRET;
+    if (!secret) {
+      console.error('JWT_SECRET is not set');
+      return null;
+    }
+
+    const parts = token.split('.');
+    if (parts.length !== 3) return null;
+
+    const [headerB64, payloadB64, signatureB64] = parts;
+
+    // Import the secret key
+    const keyData = new TextEncoder().encode(secret);
+    const key = await crypto.subtle.importKey(
+      'raw',
+      keyData,
+      { name: 'HMAC', hash: 'SHA-256' },
+      false,
+      ['verify'],
+    );
+
+    // Verify signature
+    const signatureBytes = base64UrlDecode(signatureB64).buffer as ArrayBuffer;
+    const dataToVerify = new TextEncoder().encode(`${headerB64}.${payloadB64}`);
+
+    const isValid = await crypto.subtle.verify(
+      'HMAC',
+      key,
+      signatureBytes as ArrayBuffer,
+      dataToVerify,
+    );
+    if (!isValid) return null;
+
+    // Decode payload
+    const payloadJson = new TextDecoder().decode(base64UrlDecode(payloadB64));
+    const payload = JSON.parse(payloadJson) as JWTPayload;
+
+    // Check expiry
+    if (payload.exp && Date.now() / 1000 > payload.exp) return null;
+
+    // Validate role is a known value
+    const validRoles: UserRole[] = [
+      UserRole.ADMIN,
+      UserRole.INSTRUCTOR,
+      UserRole.STUDENT,
+      UserRole.GUEST,
+    ];
+    if (!validRoles.includes(payload.role)) return null;
+
+    return payload;
+  } catch {
+    return null;
+  }
+}
+
+function base64UrlDecode(str: string): Uint8Array {
+  const base64 = str.replace(/-/g, '+').replace(/_/g, '/');
+  const padded = base64.padEnd(base64.length + ((4 - (base64.length % 4)) % 4), '=');
+  const binary = atob(padded);
+  return Uint8Array.from(binary, (c) => c.charCodeAt(0));
+}

src/middleware.ts

@@ -15,7 +15,7 @@ import {
   INTERNAL_API_REQUEST_HEADER,
 } from './lib/apiVersioning';
 
-export function middleware(request: NextRequest) {
+export async function middleware(request: NextRequest) {
   const traceId = crypto.randomUUID();
   request.headers.set('x-trace-id', traceId);
 
@@ -27,8 +27,13 @@ export function middleware(request: NextRequest) {
   }
 
   // In a real application, you would verify the JWT or session here.
-  const roleCookie = request.cookies.get('user-role')?.value as UserRole | undefined;
-  const userRole = roleCookie || null;
+  // Verify JWT from Authorization header or cookie — never trust client-supplied role cookies
+  const token =
+    request.headers.get('Authorization')?.replace('Bearer ', '') ??
+    request.cookies.get('Authorization')?.value;
+  const { verifyToken } = await import('./lib/auth/jwt');
+  const payload = await verifyToken(token);
+  const userRole = payload?.role ?? null;
 
   const withHeaders = (response: NextResponse) => {
     response.headers.set('x-trace-id', traceId);

src/middleware/__tests__/rbac.security.test.ts

@@ -0,0 +1,42 @@
+import { NextRequest } from 'next/server';
+import { checkRoutePermission } from '../rbac';
+import { UserRole } from '@/types/api';
+
+function makeRequest(pathname: string) {
+  return new NextRequest(new URL(`http://localhost${pathname}`));
+}
+
+describe('RBAC middleware — role elevation prevention', () => {
+  it('redirects to /login when no role is provided', () => {
+    const res = checkRoutePermission(makeRequest('/admin'), null);
+    expect(res?.status).toBe(307);
+    expect(res?.headers.get('location')).toContain('/login');
+  });
+
+  it('redirects to /unauthorized when STUDENT tries to access /admin', () => {
+    const res = checkRoutePermission(makeRequest('/admin'), UserRole.STUDENT);
+    expect(res?.status).toBe(307);
+    expect(res?.headers.get('location')).toContain('/unauthorized');
+  });
+
+  it('redirects to /unauthorized when INSTRUCTOR tries to access /admin', () => {
+    const res = checkRoutePermission(makeRequest('/admin'), UserRole.INSTRUCTOR);
+    expect(res?.status).toBe(307);
+    expect(res?.headers.get('location')).toContain('/unauthorized');
+  });
+
+  it('allows ADMIN to access /admin', () => {
+    const res = checkRoutePermission(makeRequest('/admin'), UserRole.ADMIN);
+    expect(res).toBeNull();
+  });
+
+  it('allows INSTRUCTOR to access /instructor', () => {
+    const res = checkRoutePermission(makeRequest('/instructor'), UserRole.INSTRUCTOR);
+    expect(res).toBeNull();
+  });
+
+  it('allows STUDENT to access /dashboard', () => {
+    const res = checkRoutePermission(makeRequest('/dashboard'), UserRole.STUDENT);
+    expect(res).toBeNull();
+  });
+});