better-auth

SKILL.md

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

Database: Install Drizzle, configure schema, run migrations

Backend: Create Better Auth instance with NestJS module

Frontend: Configure auth client, create pages, add middleware

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

Install dependencies

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

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! },
});

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)

Create database module - Set up Drizzle connection service

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!,
    }
  }
});

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)

Configure auth client (lib/auth.ts)

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

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*'] };

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}`
          });
        }
      }
    })
  ]
});

// Client: Verify TOTP and trust device
const verify2FA = async (code: string) => {
  const { data } = await authClient.twoFactor.verifyTotp({
    code,
    trustDevice: true  // Device trusted for 30 days
  });

  if (data) {
    router.push('/dashboard');
  }
};

Output: User authenticated; device trusted for 30 days without 2FA prompt.

Example 3: Passkey Registration and Login

Input: Enable passkey (WebAuthn) authentication for passwordless login.

// Server
import { passkey } from '@better-auth/passkey';
export const auth = betterAuth({
  plugins: [
    passkey({
      rpID: 'example.com',
      rpName: 'My App',
    })
  ]
});

// Client: Register passkey
const registerPasskey = async () => {
  const { data } = await authClient.passkey.register({
    name: 'My Device'
  });
};

// Client: Sign in with autofill
const signInWithPasskey = async () => {
  await authClient.signIn.passkey({
    autoFill: true,  // Browser suggests passkey
  });
};

Output: Users can register and authenticate with biometrics, PIN, or security keys.

For more examples (backup codes, organizations, magic link, conditional UI), see references/plugins.md and references/passkey.md.

Best Practices

Environment Variables: Store all secrets in .env, add to .gitignore

Secret Generation: Use openssl rand -base64 32 for BETTER_AUTH_SECRET

HTTPS Required: OAuth callbacks need HTTPS (use ngrok for local testing)

Session Expiration: Configure based on security requirements (7 days default)

Database Indexing: Add indexes on email, userId for performance

Error Handling: Return generic errors without exposing sensitive details

Rate Limiting: Add to auth endpoints to prevent brute force attacks

Type Safety: Use npx better-auth typegen for full TypeScript coverage

Constraints and Warnings

Security Notes

Never commit secrets: Add .env to .gitignore; never commit OAuth secrets or DB credentials

Validate redirect URLs: Always validate OAuth redirect URLs to prevent open redirects

Hash passwords: Better Auth handles password hashing automatically; never implement custom hashing

Session storage: For production, use Redis or another scalable session store

HTTPS Only: Always use HTTPS for authentication in production

Email Verification: Always implement email verification for password-based auth

Known Limitations

Better Auth requires Node.js 18+ for Next.js App Router support

Some OAuth providers require specific redirect URL formats

Passkeys require HTTPS and compatible browsers

Organization features require additional database tables

Resources

Documentation

Better Auth - Official documentation

Drizzle ORM - Database ORM

NestJS - Backend framework

Next.js - Frontend framework

Reference Implementations

references/nestjs-setup.md - Complete NestJS backend setup

references/nextjs-setup.md - Complete Next.js frontend setup

references/plugins.md - Plugin configuration (2FA, passkey, organizations, SSO, magic link)

references/mfa-2fa.md - Detailed MFA/2FA guide

references/passkey.md - Detailed passkey implementation

references/schema.md - Drizzle schema reference

references/social-providers.md - Social provider configuration