nextjs-security

Included with Lifetime

$97 forever

Secure Next.js App Router with middleware auth, Server Action validation, CSP headers, and taint APIs. Use when adding authentication middleware, validating Server Action inputs with Zod, or preventing secret leakage to client bundles.

Web Dev

What this skill does

# Next.js Security

## **Priority: P0 (CRITICAL)**

## Workflow: Secure Next.js App

1. **Add auth middleware** — Create `middleware.ts` to verify JWT/session on protected routes.
2. **Validate Server Actions** — Parse all inputs with Zod schemas; call `await auth()` first.
3. **Set security headers** — Add CSP, HSTS, X-Frame-Options in middleware response.
4. **Use `server-only`** — Import in modules containing secrets to prevent client bundling.
5. **Taint sensitive objects** — Use `taintObjectReference` to block server objects from reaching client.

## Secure Server Action Example

See [implementation examples](references/implementation.md)

## Implementation Guidelines

- **Next.js Middleware**: Use **`middleware.ts`** for edge-side authentication, role-based access control (RBAC), and enforcing **Security Headers** (e.g., **`Content-Security-Policy (CSP)`**, **`X-XSS-Protection`**).
- **Server Actions**: Always **sanitize all inputs** from `FormData` or JSON using **Zod**. Perform **authentication checks** (`await auth()`) inside every action to verify caller.
- **Data Tainting**: Use **`experimental_taint`** API (**`taintObjectReference`**) to ensure sensitive server objects (e.g., User with `passwordHash`) never leak into Client Component.
- **Route Handlers (`route.ts`)**: Implement **rate limiting** to prevent brute-force or DoS attacks. Verify **Origin/Referer headers** to mitigate **CSRF** (Cross-Site Request Forgery).
- **Auth Tokens**: strictly use **`HttpOnly`, `Secure` cookies** with **`SameSite: 'Lax'`** for session management. Never store tokens in `localStorage`.
- **Logic Isolation**: use **`server-only`** package to prevent backend-specific logic from included in client bundle.
- **Component Purity**: **Escape all user-provided content** rendered in components. Never use **`dangerouslySetInnerHTML`** without sanitizer like **`DOMPurify`**.

## Anti-Patterns

- **No leaking DB fields to client**: Use DTOs; never pass raw model objects.
- **No `process.env` in client bundles**: Mark as `NEXT_PUBLIC_` only if safe to expose.
- **No unvalidated Server Action inputs**: Always validate with Zod schema.
- **No auth checks in shared Layouts**: Auth in layouts insecure; use Middleware.

## References

- [Secure App Router Patterns](references/implementation.md)

Files: 3

Size: 5.8 KB

Complexity: 25/100

Category: Web Dev

Source: https://github.com/hoangnguyen0403/agent-skills-standard/tree/main/skills/nextjs/nextjs-security

Related in Web Dev

generating-lwc-components

Included

Lightning Web Components with PICKLES methodology and 165-point scoring. Use this skill when the user creates or edits LWC components, builds wire service patterns, or writes Jest tests for LWC. TRIGGER when: user creates/edits LWC components, touches lwc/**/*.js, .html, .css, .js-meta.xml files, or asks about wire service, SLDS, or Jest LWC tests. DO NOT TRIGGER when: Apex classes (use generating-apex), Aura components, or Visualforce.

Web Devscripts

tanstack-query

Included

Manage server state in React with TanStack Query v5. Set up queries with useQuery, mutations with useMutation, configure QueryClient caching strategies, implement optimistic updates, and handle infinite scroll with useInfiniteQuery. Use when: setting up data fetching in React projects, migrating from v4 to v5, or fixing object syntax required errors, query callbacks removed issues, cacheTime renamed to gcTime, isPending vs isLoading confusion, keepPreviousData removed problems.

Web Devscripts

document-processor-api

Included

Process documents with Nutrient DWS. Use when the user wants to generate PDFs from HTML or URLs, convert Office/images/PDFs, assemble or split packets, OCR scans, extract text/tables/key-value pairs, redact PII, watermark, sign, fill forms, optimize PDFs, or produce compliance outputs like PDF/A or PDF/UA. Triggers include convert to PDF, merge these PDFs, OCR this scan, extract tables, redact PII, sign this PDF, make this PDF/A, or linearize for web delivery.

Web Devscripts

nutrient-document-processing

Included

Web Devscripts

tanstack-query

Included

Manage server state in React with TanStack Query v5. Covers useMutationState, simplified optimistic updates, throwOnError, network mode (offline/PWA), and infiniteQueryOptions. Use when setting up data fetching, fixing v4→v5 migration errors (object syntax, gcTime, isPending, keepPreviousData), or debugging SSR/hydration issues with streaming server components.

Web Devscripts

accelint-nextjs-best-practices

Included

Next.js performance optimization and best practices. Use when writing Next.js code (App Router or Pages Router); implementing Server Components, Server Actions, or API routes; optimizing RSC serialization, data fetching, or server-side rendering; reviewing Next.js code for performance issues; fixing authentication in Server Actions; or implementing Suspense boundaries, parallel data fetching, or request deduplication.

Web Devscripts