mern-add-auth

name	mern-add-auth
description	Add authentication to a MERN project using NextAuth.js with OAuth and/or credentials.
argument-hint	[--providers google,github,credentials] [--with-user-model]
allowed-tools	Bash, Write, Read, Glob, Grep

Purpose

Add secure authentication to an existing MERN project using NextAuth.js (Auth.js).

Arguments

• --providers <list> — Comma-separated providers (default: google,github)
  • Options: google, github, discord, credentials
• --with-user-model — Create User model in MongoDB for storing user data

What gets created

apps/web/
├── app/api/auth/[...nextauth]/route.ts   # NextAuth API route
├── src/lib/auth.ts                        # Auth config + providers
├── src/lib/auth-client.ts                 # Client-side helpers
├── src/components/auth/
│   ├── SignInButton.tsx                   # OAuth sign-in
│   ├── SignOutButton.tsx                  # Sign-out
│   └── UserMenu.tsx                       # User avatar + dropdown
├── src/server/db/models/user.ts           # (if --with-user-model)
└── middleware.ts                          # Route protection

packages/shared/schemas/
└── user.ts                                # User schemas

.env.example                               # Updated with auth vars

Environment variables required

# OAuth (per provider)
GOOGLE_CLIENT_ID=
GOOGLE_CLIENT_SECRET=
GITHUB_CLIENT_ID=
GITHUB_CLIENT_SECRET=

# NextAuth
NEXTAUTH_URL=http://localhost:3000
NEXTAUTH_SECRET=  # Generate with: openssl rand -base64 32

Workflow

1. Install dependencies: next-auth, @auth/mongodb-adapter (if using DB)
2. Create auth config with selected providers
3. Create API route handler
4. Create auth components
5. Create middleware for protected routes
6. Update env.ts schema with auth variables
7. Create User model (if --with-user-model)
8. Add session provider to app layout
9. Run tests to verify

Protected routes

Middleware protects routes matching these patterns by default:

• /dashboard/*
• /settings/*
• /api/* (except /api/auth/* and /api/health)

Customize in middleware.ts.

Usage patterns

Server Component

import { getServerSession } from 'next-auth';
import { authOptions } from '@/lib/auth';

const session = await getServerSession(authOptions);
if (!session) redirect('/api/auth/signin');

Client Component

'use client';
import { useSession } from 'next-auth/react';

const { data: session, status } = useSession();

API Route

const session = await getServerSession(authOptions);
if (!session?.user?.id) {
  return NextResponse.json(err('UNAUTHORIZED', 'Authentication required'), { status: 401 });
}

Output

Summarize: providers configured, environment variables needed, protected routes, components available.

Reference

For templates and OAuth setup guides, see reference/mern-add-auth-reference.md