ck-better-auth

name	ck:better-auth
description	Add authentication with Better Auth (TypeScript). Use for email/password, OAuth providers (Google, GitHub), 2FA/MFA, passkeys/WebAuthn, sessions, RBAC, rate limiting.
user-invocable	true
when_to_use	Invoke for Better Auth setup, sessions, OAuth, MFA, or RBAC.
category	backend
keywords	["auth","oauth","2fa","passkeys","sessions"]
license	MIT
argument-hint	[auth-method or feature]
metadata	{"author":"claudekit","version":"2.0.0"}

Better Auth Skill

Better Auth is comprehensive, framework-agnostic authentication/authorization framework for TypeScript with built-in email/password, social OAuth, and powerful plugin ecosystem for advanced features.

When to Use

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

Quick Start

Installation

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

Environment Setup

Create .env:

BETTER_AUTH_SECRET=<generated-secret-32-chars-min>
BETTER_AUTH_URL=http://localhost:3000

Basic Server Setup

Create auth.ts (root, lib/, utils/, or under src/app/server/):

import { betterAuth } from "better-auth";

export const auth = betterAuth({
  database: {
    // See references/database-integration.md
  },
  emailAndPassword: {
    enabled: true,
    autoSignIn: true
  },
  socialProviders: {
    github: {
      clientId: process.env.GITHUB_CLIENT_ID!,
      clientSecret: process.env.GITHUB_CLIENT_SECRET!,
    }
  }
});

Database Schema

npx @better-auth/cli generate  # Generate schema/migrations
npx @better-auth/cli migrate   # Apply migrations (Kysely only)

Mount API Handler

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);

Other frameworks: See references/email-password-auth.md#framework-setup

Client Setup

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"
});

Basic Usage

// Sign up
await authClient.signUp.email({
  email: "[e-mail]",
  password: "secure123",
  name: "John Doe"
});

// Sign in
await authClient.signIn.email({
  email: "[e-mail]",
  password: "secure123"
});

// OAuth
await authClient.signIn.social({ provider: "github" });

// Session
const { data: session } = authClient.useSession(); // React/Vue/Svelte
const { data: session } = await authClient.getSession(); // Vanilla JS

Feature Selection Matrix

Feature	Plugin Required	Use Case	Reference
Email/Password	No (built-in)	Basic auth	email-password-auth.md
OAuth (GitHub, Google, etc.)	No (built-in)	Social login	oauth-providers.md
Email Verification	No (built-in)	Verify email addresses	email-password-auth.md
Password Reset	No (built-in)	Forgot password flow	email-password-auth.md
Two-Factor Auth (2FA/TOTP)	Yes (twoFactor)	Enhanced security	advanced-features.md
Passkeys/WebAuthn	Yes (passkey)	Passwordless auth	advanced-features.md
Magic Link	Yes (magicLink)	Email-based login	advanced-features.md
Username Auth	Yes (username)	Username login	email-password-auth.md
Organizations/Multi-tenant	Yes (organization)	Team/org features	advanced-features.md
Rate Limiting	No (built-in)	Prevent abuse	advanced-features.md
Session Management	No (built-in)	User sessions	advanced-features.md

Auth Method Selection Guide

Choose Email/Password when:

• Building standard web app with traditional auth
• Need full control over user credentials
• Targeting users who prefer email-based accounts

Choose OAuth when:

• Want quick signup with minimal friction
• Users already have social accounts
• Need access to social profile data

Choose Passkeys when:

• Want passwordless experience
• Targeting modern browsers/devices
• Security is top priority

Choose Magic Link when:

• Want passwordless without WebAuthn complexity
• Targeting email-first users
• Need temporary access links

Combine Multiple Methods when:

• Want flexibility for different user preferences
• Building enterprise apps with various auth requirements
• Need progressive enhancement (start simple, add more options)

Core Architecture

Better Auth uses client-server architecture:

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

Implementation Checklist

• Install better-auth package
• Set environment variables (SECRET, URL)
• Create auth server instance with database config
• Run schema migration (npx @better-auth/cli generate)
• Mount API handler in framework
• Create client instance
• Implement sign-up/sign-in UI
• Add session management to components
• Set up protected routes/middleware
• Add plugins as needed (regenerate schema after)
• Test complete auth flow
• Configure email sending (verification/reset)
• Enable rate limiting for production
• Set up error handling

Current Security Notes

Recent Better Auth releases tightened several security-sensitive plugin paths. When enabling these features, verify the installed version includes the current fixes and keep the default safer settings unless the app has an explicit threat-model exception:

• oidc-provider and mcp plugins: confidential clients must require client_secret on refresh-token grants; use constant-time secret comparison and reject incomplete PKCE parameters.
• magicLink: verification tokens are single-use; avoid custom flows that mint multiple sessions from concurrent requests.
• Organizations/invitations: keep requireEmailVerificationOnInvitation enabled so unverified email ownership cannot accept or enumerate invitations.
• Device authorization: bind pending device codes to the verifying session so one authenticated user cannot approve another user's device flow.

Reference Documentation

Core Authentication

• Email/Password Authentication - Email/password setup, verification, password reset, username auth
• OAuth Providers - Social login setup, provider configuration, token management
• Database Integration - Database adapters, schema setup, migrations

Advanced Features

• Advanced Features - 2FA/MFA, passkeys, magic links, organizations, rate limiting, session management

Scripts

• scripts/better_auth_init.py - Initialize Better Auth configuration with interactive setup

Resources

• Docs: 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