Auth0 vs AuthJS for Solo Developers

Quick Comparison

Auth0 Overview

Auth0 is Okta's enterprise identity platform. It's a fully managed auth service covering social logins, passwordless, MFA, SAML SSO, machine-to-machine tokens, and role-based access. The Universal Login redirects users to Auth0's domain for authentication, so credentials never touch your server.

Configuration is done through their dashboard: creating applications, wiring up social connections, and writing Actions (serverless hooks) to customize login flows. The SDK ecosystem covers React, Vue, Angular, Django, Rails, Express, and mobile frameworks.

I set up Auth0 for a multi-tenant B2B app. The SAML SSO integration with a customer's Okta instance took half a day, but after that, enterprise login just worked. For that specific use case, Auth0 earned every dollar.

AuthJS Overview

AuthJS (formerly NextAuth.js) is an open-source authentication library for JavaScript frameworks. It started as a Next.js-only solution but now supports SvelteKit, Express, and more. You configure providers, define callbacks, and AuthJS handles OAuth flows, session management, and CSRF protection.

The big appeal is that AuthJS is free and runs in your application. No external service, no monthly bill, no MAU limits. You add providers (Google, GitHub, Discord, email), configure a database adapter if you want persistent sessions, and auth works. The library handles the OAuth dance, token exchange, and session cookies.

I've used AuthJS in multiple Next.js projects. Adding Google and GitHub sign-in takes about 30 minutes, including the OAuth app creation on each provider's side. The session hook gives you user data on every page. For straightforward social login, AuthJS removes nearly all the friction.

Key Differences

Cost. AuthJS is completely free. No limits, no tiers, no per-user charges. Auth0 gives you 7,500 MAU free, then charges $35/month for Essential. As your app grows, Auth0's costs scale with your user count. AuthJS costs nothing regardless of how many users you have. For a bootstrapping solo developer, this matters.

Managed vs library. Auth0 handles everything: hosting, security patches, uptime, and compliance. AuthJS is a library in your codebase. You're responsible for keeping it updated, handling edge cases, and ensuring your session storage is reliable. Auth0 removes operational burden. AuthJS removes vendor dependency.

Social login setup. Both make social logins straightforward, but the experience differs. Auth0 lets you toggle providers in a dashboard and enter your OAuth credentials. AuthJS requires you to configure each provider in code and handle the callback routes. Auth0 is slightly faster for adding new providers. AuthJS gives you more control over the flow.

Enterprise features. Auth0 has SAML SSO, SCIM provisioning, organizations, and compliance certifications. AuthJS has none of this built in. You could build SAML support on top of AuthJS using additional libraries, but it's a significant effort. If enterprise customers need SSO, Auth0 is the realistic choice.

Framework support. AuthJS supports Next.js, SvelteKit, and Express with official adapters. Auth0 has SDKs for nearly every framework and language. If you're working in Python, Ruby, Go, or mobile, Auth0 has you covered. AuthJS is JavaScript-only.

Customization. AuthJS gives you callbacks at every step of the auth flow: sign-in, JWT creation, session generation. You can modify tokens, add custom claims, redirect users, and control session behavior in code. Auth0 offers similar customization through Actions, but you're writing serverless functions in their platform, not in your codebase.

When to Choose Auth0

• You need enterprise SSO (SAML, SCIM) for B2B customers
• Compliance certifications are a hard requirement
• You're working in a non-JavaScript framework
• You want a managed service so you don't maintain auth infrastructure
• You need features like passwordless or phone-based authentication

When to Choose AuthJS

• You're building with Next.js or SvelteKit and want free auth
• Your budget is tight and per-MAU pricing is a concern
• You want auth logic in your codebase, not on a third-party platform
• Social login (Google, GitHub, Discord) covers your needs
• You prefer open-source solutions you can audit and modify

The Verdict

For solo developers building with Next.js or SvelteKit, AuthJS is the practical choice. It's free, it's in your codebase, and it handles social logins without any recurring costs. The community is active, the documentation is solid, and most authentication needs for indie products are covered.

Auth0 makes sense when you're building for enterprise. SAML SSO, compliance, and organization management are features AuthJS simply doesn't have. If your go-to-market involves selling to companies that require SSO, Auth0 solves a real problem.

My recommendation: start with AuthJS for your MVP. It costs nothing and handles the auth patterns most solo developers need. If enterprise customers start asking for SSO, you can add Auth0 for those specific flows later. Don't pay for enterprise auth before you have enterprise customers.