Supabase Auth vs AuthJS for Solo Developers

Comparing Supabase Auth and AuthJS for solo developers. Features, pricing, pros and cons, and which one to pick for your next project.

Quick Comparison

Feature	Supabase Auth	AuthJS
Type	Auth built into Supabase platform (GoTrue server, MIT)	Open-source auth library you run inside your app
Latest version	supabase-js 2.106.2	next-auth 4.24.14 (stable), v5 in 5.0.0-beta.31
License	MIT (supabase/auth server)	ISC
Pricing	Free up to 50,000 MAU, then Pro from $25/mo (100,000 MAU included, $0.00325 per MAU over)	Free, no usage cap on the library itself
Built-in OAuth providers	About 20 major providers	Over 80 preconfigured
Learning Curve	Easy	Easy-Moderate
Best For	Full-stack apps using Supabase as backend	Next.js/SvelteKit apps using any backend
Solo Dev Rating	9/10	8/10

Supabase Auth Overview

Supabase Auth is the authentication layer of the Supabase platform. It supports email/password, magic links, phone auth, and social OAuth providers. The standout feature is Row Level Security integration: PostgreSQL policies reference auth.uid() to enforce access control at the database level, not in application code.

The free tier allows 50,000 MAU. User data lives in your PostgreSQL database in the auth schema, which you own and can query directly. The Supabase client handles session management, token refresh, and auth state automatically.

I use Supabase Auth in a project where the backend is entirely Supabase. Users sign in, RLS policies kick in, and every database query is automatically scoped to the authenticated user. No custom authorization middleware required.

AuthJS Overview

AuthJS (formerly NextAuth.js) is an open-source auth library for JavaScript frameworks. Official adapters exist for Next.js, SvelteKit, and Express. You configure OAuth providers, optionally connect a database adapter for persistent sessions, and AuthJS manages the OAuth flows, CSRF protection, and session cookies.

AuthJS is completely free with no usage limits. It supports over 60 OAuth providers: Google, GitHub, Discord, Twitch, Spotify, and dozens more. The callback system lets you customize tokens, sessions, and sign-in behavior in your application code.

I've used AuthJS in Next.js projects where the backend wasn't Supabase. Adding Google and GitHub sign-in took about 30 minutes. The useSession() hook provides auth state anywhere in the app. For web apps that need flexible, free auth, AuthJS delivers consistently.

Key Differences

Backend coupling. Supabase Auth is part of the Supabase platform. Choosing it means your database is Supabase PostgreSQL, your real-time is Supabase, and your storage is Supabase. AuthJS is independent. Use it with Prisma and PlanetScale, or Drizzle and Neon, or no database at all (JWT sessions). AuthJS doesn't care what your backend looks like.

Row Level Security. Supabase Auth's killer feature is RLS. Write a policy like auth.uid() = user_id, and your database enforces it on every query. This eliminates authorization bugs at the code level because the database handles access control. AuthJS doesn't integrate with your database's security layer. You write authorization checks in your application code.

Free tier. Supabase Auth gives you 50,000 monthly active users on the Supabase free plan. Cross the line and you move to Pro, which starts at $25 per month, includes 100,000 MAU, and bills $0.00325 per MAU beyond that. AuthJS has no usage cap on the library itself, though you might pay for the database adapter you connect (a hosted Postgres, for example) and for whatever email provider sends your magic links, since the Supabase built-in email service is rate limited and not meant for production traffic. In practice both are free for most solo developers, but the Supabase MAU meter exists while the AuthJS library has nothing to meter.

OAuth provider count. AuthJS ships with over 80 preconfigured providers, and its team actively tests roughly 20 of the most popular ones in their example app. Supabase Auth supports about 20 providers. If you need authentication through Twitch, Spotify, Notion, or other niche providers, AuthJS likely has an adapter already. Supabase covers the major providers but not the long tail.

Magic links. Supabase Auth has built-in magic link authentication. Users enter their email, receive a link, click it, and they're logged in. No password needed. AuthJS supports email-based login through providers like Resend or Nodemailer, but the setup requires more configuration. Supabase's magic links work out of the box.

Session customization. AuthJS gives you callbacks to modify JWT tokens and session objects at every step. You can add custom claims, change session duration, and control sign-in behavior programmatically. Supabase Auth manages sessions through its client with less granular control. If you need custom session logic, AuthJS is more flexible.

Framework support. AuthJS works with Next.js, SvelteKit, and Express. Supabase Auth works with any framework through its JavaScript client, plus official libraries for React Native, Flutter, Swift, and Kotlin. Supabase has broader platform support, especially for mobile.

When to Choose Supabase Auth

You're using Supabase for your database and backend
Row Level Security for database-level access control is appealing
Magic link authentication is a feature you want
You're building for mobile (Supabase has React Native, Flutter, Swift SDKs)
You want auth integrated with your database platform

When to Choose AuthJS

You're using a non-Supabase backend (PlanetScale, Neon, your own Postgres)
You need 60+ OAuth providers (Twitch, Spotify, Discord, etc.)
Session and token customization via callbacks is important
You want auth completely independent from your database choice
You're building with Next.js and want the tightest framework integration

The Verdict

If you're using Supabase as your backend, use Supabase Auth. The RLS integration alone makes this decision easy. Having your database enforce access control based on the authenticated user is a powerful feature that eliminates bugs. Adding AuthJS on top of Supabase would mean losing this integration.

If you're NOT using Supabase, AuthJS is the stronger pick for Next.js and SvelteKit projects. It's free, supports more providers, and gives you more control over sessions and tokens. You're not coupled to any platform, and the callback system handles most customization needs.

My recommendation: let your backend choice drive this. Using Supabase? Use Supabase Auth. Using anything else? Use AuthJS. Both are excellent, and the right answer depends entirely on what's behind your frontend. Don't overthink it. Pick the one that fits your stack and move on to building your product.

By the Numbers (2026)

Here is where each project actually stands as of late May 2026, with sources linked at the bottom.

Versions and licenses. The Supabase JavaScript client @supabase/supabase-js is on 2.106.2, and the auth server behind it (supabase/auth, the project formerly known as GoTrue) is MIT licensed. AuthJS publishes two lines: next-auth is on 4.24.14 as the current stable release, while the v5 rewrite sits at 5.0.0-beta.31, and the framework-agnostic core @auth/core is on 0.34.3. AuthJS is ISC licensed.

Adoption on npm. In the week ending 2026-05-28, @supabase/supabase-js pulled 19,829,221 downloads. That number covers the whole Supabase client, not auth alone, so treat it as a ceiling rather than an auth-only count. On the AuthJS side, next-auth did 4,282,274 weekly downloads and the newer @auth/core did 3,152,405. Both are heavily used, and the split tells you the v4 to v5 migration is still in progress across the ecosystem.

GitHub footprint. The nextauthjs/next-auth repo sits at 28,258 stars with 4,042 forks. Supabase is a different shape: the umbrella supabase/supabase repo has 103,192 stars (Apache-2.0), but the actual auth server supabase/auth is a smaller, focused 2,442-star repo. Stars on the monorepo reflect the whole platform, not the auth piece, which is worth remembering when you compare the two head to head.

Providers. AuthJS comes with over 80 preconfigured OAuth providers and actively tests around 20 of the most popular ones. Supabase Auth covers roughly 20 of the major providers. For mainstream sign-in (Google, GitHub, Apple) both are fine. For the long tail, AuthJS wins on breadth.

Pricing. Supabase Auth is free up to 50,000 MAU on the free plan. Pro starts at $25 per month, includes 100,000 MAU, and charges $0.00325 per MAU above that. AuthJS has no per-user pricing because it is a library you run yourself.

Real Cost at Solo-Dev Scale

The library itself is free in both cases. The real question is what the MAU meter does to you as your app grows, because that is the only line item where these two genuinely diverge.

Take three workloads and run them through Supabase's published rates. Remember that AuthJS adds zero auth-service cost at every tier; you only ever pay for the database and email provider you choose, which you would pay for regardless of your auth library.

8,000 MAU (early traction). Supabase: $0, comfortably inside the 50,000 free-plan allowance. AuthJS: $0 for auth. Tie.

60,000 MAU (past the free line). Supabase: you are over the 50,000 free cap, so you move to Pro at $25 per month. You are still under the 100,000 MAU that Pro includes, so the bill is the flat $25 base. AuthJS: $0 for auth, plus whatever your existing Postgres and email already cost.

150,000 MAU (real product). Supabase: $25 base, plus 50,000 MAU over the 100,000 Pro allowance at $0.00325 each, which is 50,000 times $0.00325 equals $162.50, for a total of $187.50 per month in auth-attributable cost. AuthJS: still $0 for the auth library.

The takeaway is not that Supabase is expensive, because $187.50 to authenticate 150,000 active users is cheap for what you get, and that figure also buys you the database, storage, and realtime in the same plan. The takeaway is that the cost is real and it scales with your users, whereas AuthJS keeps auth itself at zero and pushes your variable cost onto infrastructure you were already paying for. If you want one bill that handles everything, Supabase. If you want to keep auth off the invoice entirely and you already run your own database, AuthJS.