Add Authentication (Auth.js)

Use this skill when the user asks to add authentication, login, sign-up, OAuth, or session management.

Steps

1. Install dependencies

   npm install next-auth@beta
   

2. Generate an auth secret

   npx auth secret
   

   This adds AUTH_SECRET to .env.local.

3. Create the auth config — create auth.ts in the project root:

   import NextAuth from "next-auth";
   import GitHub from "next-auth/providers/github";
   import Google from "next-auth/providers/google";
   
   export const { handlers, signIn, signOut, auth } = NextAuth({
     providers: [GitHub, Google],
   });
   

4. Add the route handler — create app/api/auth/[...nextauth]/route.ts:

   import { handlers } from "@/auth";
   export const { GET, POST } = handlers;
   

5. Add environment variables for each provider:

   AUTH_SECRET=...
   AUTH_GITHUB_ID=...
   AUTH_GITHUB_SECRET=...
   AUTH_GOOGLE_ID=...
   AUTH_GOOGLE_SECRET=...
   

6. Add sign-in/sign-out UI — create components that call the signIn and signOut server actions, or use <Link href="/api/auth/signin">.

7. Protect routes — use the auth() function in server components or middleware:

   import { auth } from "@/auth";
   
   export default async function ProtectedPage() {
     const session = await auth();
     if (!session) redirect("/api/auth/signin");
     return <div>Welcome {session.user?.name}</div>;
   }
   

8. Add database adapter (optional) — if the user needs persistent sessions or user records, install a database adapter (e.g. @auth/drizzle-adapter, @auth/prisma-adapter) and configure it in the auth config.

Notes

• Auth.js v5 works with Next.js App Router and Server Actions natively.
• For Pages Router, use getServerSession in getServerSideProps and useSession on the client.
• Add NEXTAUTH_URL for production deployments.
• Store minimal user data in the session; fetch full profiles from the database when needed.