Auth.js v5 with Next.js 16: The Complete Authentication Guide (2026)

Auth.js v5 (formerly NextAuth) is a complete rewrite. Most tutorials online are still for v4. Here's the definitive guide for v5 with Next.js 16 App Router. Why v5? Auth.js v5 brings: Native App Router support Better TypeScript types Edge runtime compatibility Simpler configuration Built-in CSRF protection Installation npm install next-auth@beta @auth/prisma-adapter The auth configuration Create a single auth config file that exports everything: // src/lib/auth.ts import NextAuth from " next-auth " ; import { PrismaAdapter } from " @auth/prisma-adapter " ; import Google from " next-auth/providers/google " ; import GitHub from " next-auth/providers/github " ; import Credentials from " next-auth/providers/credentials " ; import { db } from " @/lib/db " ; export const { handlers , signIn , signOut , auth } = NextAuth ({ adapter : PrismaAdapter ( db ), session : { strategy : " jwt " }, pages : { signIn : " /login " , error : " /login " , }, providers : [ Google ({ clientId : process . env