This is Day 9 of Building SaaS Solo - Design, Implementation, and Operation Advent Calendar 2025.

Yesterday I wrote about "Database Migration Operations." Today I’ll explain why I migrated my authentication library from NextAuth.js to Better Auth.

🎯 What Triggered the Migration

NextAuth.js (now Auth.js) is the de facto standard for implementing authentication in Next.js. I was also using NextAuth.js initially.

The trigger for my migration decision was a major announcement in September 2025.

Auth.js Team Joins Better Auth

In September 2025, it was announced that the Auth.js (formerly NextAuth.js) development team would be joining Better Auth.

https://www.better-auth.com/blog/authjs-joins-better-auth

Auth.js will continue to receive security patches and critical updates, but Better Auth is now recommended for new projects.

Seeing this announcement, I decided it would be better to migrate early considering future development direction.

🔑 Better Auth Features

Better Auth is an authentication library designed with a TypeScript-first approach.

Rich Feature Set

Better Auth provides various authentication features as plugins.

• Email/Password Authentication
• Social Login (Google, GitHub, X, etc.)
• Two-Factor Authentication (2FA)
• Organization/Team Management
• Magic Link Authentication
• Passkey Support

Since you can add features as plugins, you can start with a simple configuration and expand as needed.

Framework Agnostic

Better Auth works with various frameworks beyond Next.js, including Nuxt, SvelteKit, Hono, and Express.

Since I implement my API with Hono, the framework-agnostic nature was also appealing.

Drizzle ORM Integration

Better Auth can integrate directly with Drizzle ORM. Since my project uses Drizzle ORM, being able to manage authentication tables the same way is convenient.

🔄 Authentication Options

For a Next.js + Supabase setup, there are several authentication options.

Fully Managed Services

Auth0, Clerk, Kinde and other fully managed services are options that delegate all authentication to external services.

Benefits:

• Easy setup
• Maintained by security experts
• Rich features available immediately

Drawbacks:

• Free tiers exist, but costs increase with user count
• High dependency on external services
• Limited customization flexibility

Fully managed services offer peace of mind by handling security and operations, but considering long-term costs and dependencies, I ruled them out this time.

Supabase Auth Features

Supabase has a built-in authentication feature called Supabase Auth. If you’re using Supabase, this is also an option.

Benefits:

• Built into Supabase, minimal additional setup
• Easy integration with RLS (Row Level Security)
• Manage authentication from Supabase Studio

Drawbacks:

• Depends on Supabase (makes future migration difficult)
• Limited customization flexibility
• Authentication logic is on the Supabase side, harder to understand

Better Auth Features

Better Auth is a library that lets you manage authentication logic in your own code.

Benefits:

• Framework and DB agnostic (easy to migrate)
• High customization flexibility
• Authentication logic managed in code
• Extensible through plugins

Drawbacks:

• Initial setup required
• Supabase RLS integration must be implemented yourself

Why I Chose Better Auth

Aspect	Supabase Auth	Better Auth
Dependency	Strongly depends on Supabase	DB/Framework agnostic
Customization	Limited	High flexibility
Auth Logic	Supabase side	Managed in your code
Future Migration	Difficult	Easy

The main reason I chose Better Auth was that I wanted to keep future options open.

Supabase is an excellent service, but if I depend on Supabase for authentication too, the impact becomes significant if I want to migrate the database in the future. By managing authentication logic in my own code, I can keep infrastructure options flexible.

Also, managing authentication tables with Drizzle ORM allows me to handle the entire application schema uniformly, which was another advantage.

📦 Migration Overview

Before Migration

Auth: NextAuth.js
DB: Prisma Adapter → Supabase

After Migration

Auth: Better Auth
DB: Drizzle Adapter → Supabase

Basic Setup

The basic setup for Better Auth is simple.

// lib/auth.ts
import { betterAuth } from "better-auth"
import { drizzleAdapter } from "better-auth/adapters/drizzle"
import { db } from "@/db"

export const auth = betterAuth({
database: drizzleAdapter(db, {
provider: "pg",
}),
emailAndPassword: {
enabled: true,
},
socialProviders: {
google: {
clientId: process.env.GOOGLE_CLIENT_ID!,
clientSecret: process.env.GOOGLE_CLIENT_SECRET!,
},
},
})

// lib/auth-client.ts
import { createAuthClient } from "better-auth/client"

export const authClient = createAuthClient({
baseURL: process.env.NEXT_PUBLIC_APP_URL,
})

export const { signIn, signOut, useSession } = authClient

For detailed implementation, the official documentation is comprehensive.

https://www.better-auth.com/docs

💡 Migration Considerations

Migrating Existing User Data

Since NextAuth.js and Better Auth have different table structures, existing user data migration is required.

Better Auth’s official documentation has a migration guide from Auth.js (NextAuth.js).

https://www.better-auth.com/docs/guides/next-auth-migration-guide

Re-login Required

Due to different session management methods, existing users need to re-login after migration.

In my case, I migrated before release, so there was no impact. If migrating after release, consider that users will need to re-login.

✅ Summary

Here’s a summary of the main reasons for migrating from NextAuth.js to Better Auth.

Reasons for Migration:

• Auth.js development team joined Better Auth (promising future direction)
• Rich features (2FA, organization management, passkeys, etc.)
• Framework agnostic (easy integration with Hono)
• Drizzle ORM integration

Considerations:

• Existing user data migration required
• Re-login required

Better Auth is still a relatively new library, but with the Auth.js team joining, future development looks promising.

Tomorrow I’ll explain "App Router Directory Design."

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Other Articles in This Series

• Day 8: Database Migration Operations: Safely Managing Dev and Production Environments
• Day 10: App Router Directory Design: Next.js Project Structure Best Practices