Better Auth Skill

Better Auth is a comprehensive, framework-agnostic authentication and authorization framework for TypeScript that provides built-in support for email/password authentication, social sign-on, and a powerful plugin ecosystem for advanced features.

When to Use This Skill

Use this skill when:

• Implementing authentication in TypeScript/JavaScript applications
• Adding email/password or social OAuth authentication
• Setting up 2FA, passkeys, magic links, or other advanced auth features
• Building multi-tenant applications with organization support
• Implementing session management and user management
• Working with any framework (Next.js, Nuxt, SvelteKit, Remix, Astro, Hono, Express, etc.)

Core Concepts

Key Features

• Framework Agnostic: Works with any framework (Next.js, Nuxt, Svelte, Remix, Hono, Express, etc.)
• Built-in Auth Methods: Email/password and OAuth 2.0 social providers
• Plugin Ecosystem: Easy-to-add advanced features (2FA, passkeys, magic link, username, email OTP, organization, etc.)
• Database Flexibility: Supports SQLite, PostgreSQL, MySQL, MongoDB, and more
• ORM Support: Built-in adapters for Drizzle, Prisma, Kysely, and MongoDB
• Type Safety: Full TypeScript support with excellent type inference
• Session Management: Built-in session handling for both client and server

Architecture

Better Auth follows a client-server architecture:

1. Server Instance (better-auth): Handles auth logic, database operations, and API routes
2. Client Instance (better-auth/client): Provides hooks and methods for authentication
3. Plugins: Extend both server and client functionality

Installation & Setup

Step 1: Install Package

npm install better-auth
# or
pnpm add better-auth
# or
yarn add better-auth
# or
bun add better-auth

Step 2: Environment Variables

Create .env file:

BETTER_AUTH_SECRET=<generated-secret-key>
BETTER_AUTH_URL=http://localhost:3000

Generate secret: Use openssl or a random string generator (min 32 characters).

Step 3: Create Auth Server Instance

Create auth.ts in project root, lib/, utils/, or nested under src/, app/, or server/:

import { betterAuth } from 'better-auth';

export const auth = betterAuth({
  database: {
    // Database configuration
  },
  emailAndPassword: {
    enabled: true,
    autoSignIn: true, // Users auto sign-in after signup
  },
  socialProviders: {
    github: {
      clientId: process.env.GITHUB_CLIENT_ID!,
      clientSecret: process.env.GITHUB_CLIENT_SECRET!,
    },
    google: {
      clientId: process.env.GOOGLE_CLIENT_ID!,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET!,
    },
  },
});

Step 4: Database Configuration

Choose your database setup:

Direct Database Connection:

import { betterAuth } from 'better-auth';
import Database from 'better-sqlite3';
// or import { Pool } from "pg";
// or import { createPool } from "mysql2/promise";

export const auth = betterAuth({
  database: new Database('./sqlite.db'),
  // or: new Pool({ connectionString: process.env.DATABASE_URL })
  // or: createPool({ host: "localhost", user: "root", ... })
});

ORM Adapter:

// Prisma
import { prismaAdapter } from 'better-auth/adapters/prisma';
import { PrismaClient } from '@prisma/client';

const prisma = new PrismaClient();
export const auth = betterAuth({
  database: prismaAdapter(prisma, {
    provider: 'postgresql',
  }),
});

// Drizzle
import { drizzleAdapter } from 'better-auth/adapters/drizzle';
import { db } from '@/db';

export const auth = betterAuth({
  database: drizzleAdapter(db, {
    provider: 'pg', // or "mysql", "sqlite"
  }),
});

// MongoDB
import { mongodbAdapter } from 'better-auth/adapters/mongodb';
import { client } from '@/db';

export const auth = betterAuth({
  database: mongodbAdapter(client),
});

Step 5: Create Database Schema

Use Better Auth CLI:

# Generate schema/migration files
npx @better-auth/cli generate

# Or migrate directly (Kysely adapter only)
npx @better-auth/cli migrate

Step 6: Mount API Handler

Create catch-all route for /api/auth/*:

Next.js (App Router):

// app/api/auth/[...all]/route.ts
import { auth } from '@/lib/auth';
import { toNextJsHandler } from 'better-auth/next-js';

export const { POST, GET } = toNextJsHandler(auth);

Nuxt:

// server/api/auth/[...all].ts
import { auth } from '~/utils/auth';

export default defineEventHandler((event) => {
  return auth.handler(toWebRequest(event));
});

SvelteKit:

// hooks.server.ts
import { auth } from '$lib/auth';
import { svelteKitHandler } from 'better-auth/svelte-kit';

export async function handle({ event, resolve }) {
  return svelteKitHandler({ event, resolve, auth });
}

Hono:

import { Hono } from 'hono';
import { auth } from './auth';

const app = new Hono();
app.on(['POST', 'GET'], '/api/auth/*', (c) => auth.handler(c.req.raw));

Express:

import express from 'express';
import { toNodeHandler } from 'better-auth/node';
import { auth } from './auth';

const app = express();
app.all('/api/auth/*', toNodeHandler(auth));

Step 7: Create Client Instance

Create auth-client.ts:

import { createAuthClient } from 'better-auth/client';

export const authClient = createAuthClient({
  baseURL: process.env.NEXT_PUBLIC_BETTER_AUTH_URL || 'http://localhost:3000',
});

Authentication Methods

Email & Password

Server Configuration:

export const auth = betterAuth({
  emailAndPassword: {
    enabled: true,
    autoSignIn: true, // default: true
  },
});

Client Usage:

// Sign Up
const { data, error } = await authClient.signUp.email(
  {
    email: 'user@example.com',
    password: 'securePassword123',
    name: 'John Doe',
    image: 'https://example.com/avatar.jpg', // optional
    callbackURL: '/dashboard', // optional
  },
  {
    onSuccess: (ctx) => {
      // redirect or show success
    },
    onError: (ctx) => {
      alert(ctx.error.message);
    },
  }
);

// Sign In
const { data, error } = await authClient.signIn.email({
  email: 'user@example.com',
  password: 'securePassword123',
  callbackURL: '/dashboard',
  rememberMe: true, // default: true
});

Social OAuth

Server Configuration:

export const auth = betterAuth({
  socialProviders: {
    github: {
      clientId: process.env.GITHUB_CLIENT_ID!,
      clientSecret: process.env.GITHUB_CLIENT_SECRET!,
    },
    google: {
      clientId: process.env.GOOGLE_CLIENT_ID!,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET!,
    },
    // Other providers: apple, discord, facebook, etc.
  },
});

Client Usage:

await authClient.signIn.social({
  provider: 'github',
  callbackURL: '/dashboard',
  errorCallbackURL: '/error',
  newUserCallbackURL: '/welcome',
});

Sign Out

await authClient.signOut({
  fetchOptions: {
    onSuccess: () => {
      router.push('/login');
    },
  },
});

Session Management

Client-Side Session

Using Hooks (React/Vue/Svelte/Solid):

// React
import { authClient } from "@/lib/auth-client";

export function UserProfile() {
  const { data: session, isPending, error } = authClient.useSession();

  if (isPending) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;

  return <div>Welcome, {session?.user.name}!</div>;
}

// Vue
<script setup>
import { authClient } from "~/lib/auth-client";
const session = authClient.useSession();
</script>

<template>
  <div v-if="session.data">{{ session.data.user.email }}</div>
</template>

// Svelte
<script>
import { authClient } from "$lib/auth-client";
const session = authClient.useSession();
</script>

<p>{$session.data?.user.email}</p>

Using getSession:

const { data: session, error } = await authClient.getSession();

Server-Side Session

// Next.js
import { auth } from './auth';
import { headers } from 'next/headers';

const session = await auth.api.getSession({
  headers: await headers(),
});

// Hono
app.get('/protected', async (c) => {
  const session = await auth.api.getSession({
    headers: c.req.raw.headers,
  });

  if (!session) {
    return c.json({ error: 'Unauthorized' }, 401);
  }

  return c.json({ user: session.user });
});

Plugin System

Better Auth's plugin system allows adding advanced features easily.

Using Plugins

Server-Side:

import { betterAuth } from 'better-auth';
import { twoFactor, organization, username } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [twoFactor(), organization(), username()],
});

Client-Side:

import { createAuthClient } from 'better-auth/client';
import { twoFactorClient, organizationClient, usernameClient } from 'better-auth/client/plugins';

export const authClient = createAuthClient({
  plugins: [
    twoFactorClient({
      twoFactorPage: '/two-factor',
    }),
    organizationClient(),
    usernameClient(),
  ],
});

After Adding Plugins:

# Regenerate schema
npx @better-auth/cli generate

# Apply migration
npx @better-auth/cli migrate

Popular Plugins

Two-Factor Authentication (2FA)

// Server
import { twoFactor } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [twoFactor()],
});

// Client
import { twoFactorClient } from 'better-auth/client/plugins';

export const authClient = createAuthClient({
  plugins: [twoFactorClient({ twoFactorPage: '/two-factor' })],
});

// Usage
await authClient.twoFactor.enable({ password: 'userPassword' });
await authClient.twoFactor.verifyTOTP({
  code: '123456',
  trustDevice: true,
});

Username Authentication

// Server
import { username } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [username()],
});

// Client
import { usernameClient } from 'better-auth/client/plugins';

// Sign up with username
await authClient.signUp.username({
  username: 'johndoe',
  password: 'securePassword123',
  name: 'John Doe',
});

Magic Link

import { magicLink } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [
    magicLink({
      sendMagicLink: async ({ email, url }) => {
        // Send email with magic link
        await sendEmail(email, url);
      },
    }),
  ],
});

Passkey (WebAuthn)

import { passkey } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [passkey()],
});

// Client
await authClient.passkey.register();
await authClient.passkey.signIn();

Organization/Multi-Tenancy

import { organization } from 'better-auth/plugins';

export const auth = betterAuth({
  plugins: [organization()],
});

// Client
await authClient.organization.create({
  name: 'Acme Corp',
  slug: 'acme',
});

await authClient.organization.inviteMember({
  organizationId: 'org-id',
  email: 'user@example.com',
  role: 'member',
});

Advanced Configuration

Email Verification

export const auth = betterAuth({
  emailVerification: {
    sendVerificationEmail: async ({ user, url }) => {
      await sendEmail(user.email, url);
    },
    sendOnSignUp: true,
  },
});

Rate Limiting

export const auth = betterAuth({
  rateLimit: {
    enabled: true,
    window: 60, // seconds
    max: 10, // requests
  },
});

Custom Session Expiration

export const auth = betterAuth({
  session: {
    expiresIn: 60 * 60 * 24 * 7, // 7 days in seconds
    updateAge: 60 * 60 * 24, // Update every 24 hours
  },
});

CORS Configuration

export const auth = betterAuth({
  advanced: {
    corsOptions: {
      origin: ['https://example.com'],
      credentials: true,
    },
  },
});

Database Schema

Core Tables

Better Auth requires these core tables:

• user: User accounts
• session: Active sessions
• account: OAuth provider connections
• verification: Email verification tokens

Auto-generate with CLI:

npx @better-auth/cli generate

Manual schema available in docs: Check /docs/concepts/database#core-schema

Best Practices

1. Environment Variables: Always use environment variables for secrets
2. HTTPS in Production: Set BETTER_AUTH_URL to HTTPS URL
3. Session Security: Use secure cookies in production
4. Error Handling: Implement proper error handling on client and server
5. Type Safety: Leverage TypeScript types for better DX
6. Plugin Order: Some plugins depend on others, check documentation
7. Database Migrations: Always run migrations after adding plugins
8. Rate Limiting: Enable rate limiting for production
9. Email Verification: Implement email verification for security
10. Password Requirements: Customize password validation as needed

Common Patterns

Protected Routes (Server-Side)

// Next.js middleware
import { auth } from '@/lib/auth';
import { NextRequest, NextResponse } from 'next/server';

export async function middleware(request: NextRequest) {
  const session = await auth.api.getSession({
    headers: request.headers,
  });

  if (!session) {
    return NextResponse.redirect(new URL('/login', request.url));
  }

  return NextResponse.next();
}

export const config = {
  matcher: ['/dashboard/:path*'],
};

User Profile Updates

await authClient.updateUser({
  name: 'New Name',
  image: 'https://example.com/new-avatar.jpg',
});

Password Management

// Change password
await authClient.changePassword({
  currentPassword: 'oldPassword',
  newPassword: 'newPassword',
});

// Reset password (forgot password)
await authClient.forgetPassword({
  email: 'user@example.com',
  redirectTo: '/reset-password',
});

await authClient.resetPassword({
  token: 'reset-token',
  password: 'newPassword',
});

Troubleshooting

Common Issues

1. "Unable to find auth instance"

   • Ensure auth.ts is in correct location (root, lib/, utils/)
   • Export auth instance as auth or default export

2. Database connection errors

   • Verify database credentials
   • Check if database server is running
   • Ensure correct adapter for your database

3. CORS errors

   • Configure corsOptions in advanced settings
   • Ensure client and server URLs match

4. Plugin not working

   • Run migrations after adding plugins
   • Check plugin is added to both server and client
   • Verify plugin configuration

Framework-Specific Guides

• Next.js: Use Next.js plugin for server actions
• Nuxt: Configure server middleware
• SvelteKit: Use hooks.server.ts
• Astro: Set up API routes properly
• Hono/Express: Use appropriate node handlers

Resources

• Documentation: https://www.better-auth.com/docs
• GitHub: https://github.com/better-auth/better-auth
• Plugins: https://www.better-auth.com/docs/plugins
• Examples: https://www.better-auth.com/docs/examples

Implementation Checklist

When implementing Better Auth:

• Install better-auth package
• Set up environment variables (SECRET, URL)
• Create auth server instance
• Configure database/adapter
• Run schema migration
• Configure authentication methods
• Mount API handler
• Create client instance
• Implement sign-up/sign-in UI
• Add session management
• Set up protected routes
• Add plugins as needed
• Test authentication flow
• Configure email sending (if needed)
• Set up error handling
• Enable rate limiting for production