/better-auth

name: better-auth
description: Provides Better Auth integration patterns for NestJS backend and Next.js frontend with Drizzle ORM and PostgreSQL. Use when setting up Better Auth with NestJS backend, integrating Next.js App Router frontend, configuring Drizzle ORM schema, implementing social login (GitHub, Google), adding plugins (2FA, Organization, SSO, Magic Link, Passkey), implementing email/password authentication with session management, or creating protected routes and middleware.
allowed-tools: Read, Write, Edit, Glob, Grep, Bash

Better Auth Integration Guide

Overview

Better Auth is a type-safe authentication framework for TypeScript supporting multiple providers, 2FA, SSO, organizations, and passkeys. This skill covers integration patterns for NestJS backend with Drizzle ORM + PostgreSQL and Next.js App Router frontend.

When to Use

• Setting up Better Auth with NestJS backend
• Integrating Next.js App Router frontend
• Configuring Drizzle ORM schema with PostgreSQL
• Implementing social login (GitHub, Google, Facebook, Microsoft)
• Adding MFA/2FA with TOTP, passkey passwordless auth, or magic links
• Managing trusted devices and backup codes for account recovery
• Building multi-tenant apps with organizations or SSO
• Creating protected routes with session management

Quick Start

Installation

# Backend (NestJS)
npm install better-auth @auth/drizzle-adapter drizzle-orm pg
npm install -D drizzle-kit

# Frontend (Next.js)
npm install better-auth

4-Phase Setup

1. **Database**: Install Drizzle, configure schema, run migrations 2. **Backend**: Create Better Auth instance with NestJS module 3. **Frontend**: Configure auth client, create pages, add middleware 4. **Plugins**: Add 2FA, passkey, organizations as needed

See `references/nestjs-setup.md` for complete backend setup, `references/plugins.md` for plugin configuration.

Instructions

Phase 1: Database Setup

1. **Install dependencies**

   npm install drizzle-orm pg @auth/drizzle-adapter better-auth
   npm install -D drizzle-kit

2. **Create Drizzle config** (`drizzle.config.ts`)

   import { defineConfig } from 'drizzle-kit';
   export default defineConfig({
     schema: './src/auth/schema.ts',
     out: './drizzle',
     dialect: 'postgresql',
     dbCredentials: { url: process.env.DATABASE_URL! },
   });

3. **Generate and run migrations**

   npx drizzle-kit generate
   npx drizzle-kit migrate

**Checkpoint**: Verify tables created: `psql $DATABASE_URL -c "\dt"` should show `user`, `account`, `session`, `verification_token` tables.

Phase 2: Backend Setup (NestJS)

1. **Create database module** - Set up Drizzle connection service

2. **Configure Better Auth instance**

   // src/auth/auth.instance.ts
   import { betterAuth } from 'better-auth';
   import { drizzleAdapter } from '@auth/drizzle-adapter';
   import * as schema from './schema';

   export const auth = betterAuth({
     database: drizzleAdapter(schema, { provider: 'postgresql' }),
     emailAndPassword: { enabled: true },
     socialProviders: {
       github: {
         clientId: process.env.AUTH_GITHUB_CLIENT_ID!,
         clientSecret: process.env.AUTH_GITHUB_CLIENT_SECRET!,
       }
     }
   });

3. **Create auth controller**

   @Controller('auth')
   export class AuthController {
     @All('*')
     async handleAuth(@Req() req: Request, @Res() res: Response) {
       return auth.handler(req);
     }
   }

**Checkpoint**: Test endpoint `GET /auth/get-session` returns `{ session: null }` when unauthenticated (no error).

Phase 3: Frontend Setup (Next.js)

1. **Configure auth client** (`lib/auth.ts`)

   import { createAuthClient } from 'better-auth/client';
   export const authClient = createAuthClient({
     baseURL: process.env.NEXT_PUBLIC_APP_URL!
   });

2. **Add middleware** (`middleware.ts`)

   import { auth } from '@/lib/auth';
   export default auth((req) => {
     if (!req.auth && req.nextUrl.pathname.startsWith('/dashboard')) {
       return Response.redirect(new URL('/sign-in', req.nextUrl.origin));
     }
   });
   export const config = { matcher: ['/dashboard/:path*'] };

3. **Create sign-in page** with form or social buttons

**Checkpoint**: Navigating to `/dashboard` when logged out should redirect to `/sign-in`.

Phase 4: Advanced Features

Add plugins from `references/plugins.md`:

• **2FA**: `twoFactor({ issuer: 'AppName', otpOptions: { sendOTP } })`
• **Passkey**: `passkey({ rpID: 'domain.com', rpName: 'App' })`
• **Organizations**: `organization({ avatar: { enabled: true } })`
• **Magic Link**: `magicLink({ sendMagicLink })`
• **SSO**: `sso({ saml: { enabled: true } })`

**Checkpoint**: After adding plugins, re-run migrations and verify new tables exist.

Examples

Example 1: Server Component with Session

**Input**: Display user data in a Next.js Server Component.

// app/dashboard/page.tsx
import { auth } from '@/lib/auth';
import { redirect } from 'next/navigation';

export default async function DashboardPage() {
  const session = await auth();

  if (!session) {
    redirect('/sign-in');
  }

  return (
    <div>
      <h1>Welcome, {session.user.name}</h1>
      <p>Email: {session.user.email}</p>
    </div>
  );
}

**Output**: Renders user info for authenticated users; redirects unauthenticated to sign-in.

Example 2: 2FA TOTP Verification with Trusted Device

**Input**: User has 2FA enabled and wants to sign in, marking device as trusted.

// Server: Configure 2FA with OTP sending
export const auth = betterAuth({
  plugins: [
    twoFactor({
      issuer: 'MyApp',
      otpOptions: {
        async sendOTP({ user, otp }, ctx) {
          await sendEmail({
            to: user.email,
            subject: 'Your verification code',
            body: `Code: ${otp}`
          });