Auth.js vs Keycloak for Solo Developers

Choosing between a lightweight library and a full identity platform is one of the most consequential auth decisions a solo developer can make. Auth.js (formerly NextAuth.js) and Keycloak sit at opposite ends of the spectrum. One is a library you add to your JavaScript framework. The other is an entire identity server you deploy and manage. Understanding when each makes sense will save you from either over-engineering or under-building your auth layer.

Auth.js Overview

Auth.js is an open-source authentication library for JavaScript frameworks. It started as NextAuth.js for Next.js and has expanded to support SvelteKit, Express, Remix, and other frameworks. It handles session management, OAuth flows, email/magic link sign-in, and credential-based login.

The library runs inside your existing application. There is no separate server to deploy. You configure providers (Google, GitHub, Discord, etc.), set up a database adapter (Prisma, Drizzle, or others), and Auth.js manages sessions using either JWTs or database sessions. The entire setup lives in a single configuration file.

For solo developers, the appeal is control without complexity. You own the code, the sessions, and the user data. There are no usage limits, no monthly active user caps, and no vendor lock-in. Auth.js is free and always will be.

Keycloak Overview

Keycloak is an enterprise-grade identity and access management server from Red Hat. It provides OAuth 2.0, OpenID Connect, SAML 2.0, LDAP integration, fine-grained RBAC, and advanced features like identity brokering and custom authentication flows.

You deploy Keycloak as a standalone Java application, configure realms, clients, and roles through its admin console, and connect your apps via standard OIDC. It is the go-to solution for organizations managing authentication across multiple applications and services.

The power comes with weight. Keycloak requires its own server, its own database, TLS configuration, and ongoing maintenance. The admin console has an enormous number of settings. For teams with dedicated DevOps resources, this is manageable. For solo developers, it is a significant commitment.

Comparison Table

By the Numbers (2026)

The headline framing of "library versus identity server" holds up, but a few current facts sharpen the picture for a solo developer making this call today.

Auth.js (next-auth). The stable line is next-auth@4.24.14, published April 2026. The big asterisk worth knowing before you commit is that the v5 rewrite is still in beta. The Auth.js docs tell Next.js users to install next-auth@beta, which currently resolves to 5.0.0-beta.31. So the "modern" entry point most tutorials point you at is technically pre-release, even though it is widely used in production. The framework-agnostic core, @auth/core, sits at 0.34.3. Adoption is not in question. next-auth pulled roughly 4.24M npm downloads in the week of May 21 to 27, 2026, and @auth/core about 3.09M in the same window. The repository carries around 28.3k GitHub stars and is written in TypeScript.

Keycloak. The current release is 26.6.2, shipped May 19, 2026, on the 26.6 feature line. It is a Java application, and the repository has around 34.6k GitHub stars. Because it is a deployed server rather than a package you import, there is no npm download metric. The relevant maturity signal instead is that Keycloak ships frequent point releases, which is also the maintenance reality you sign up for: every release is a server you patch, not a dependency a bot bumps for you.

The takeaway from the raw numbers: both projects are healthy and heavily used, so neither choice is a bet on an abandoned tool. Auth.js's enormous download count reflects how many JavaScript apps reach for the path of least resistance, while Keycloak's higher star count reflects its standing as the default open-source identity server for teams that need one. Stars measure attention. Downloads measure how many apps actually ship with the thing. Read them accordingly.

Which One Ships Faster for a Solo Dev

Both tools are free and open source, so cost is not the deciding factor. The real currency for a solo developer is time, both the hours to first working login and the hours you keep paying every month after launch. Here is a grounded way to choose.

Time to first login. Auth.js lives inside your app. You install one package, add a config file with your providers, wire up a database adapter if you want persistent sessions, and you have working OAuth. The post estimates 30 minutes, and that is realistic for a single social provider on a supported framework. Keycloak is a separate server. Before a single user logs in you provision a host, run the Java server, attach a database, terminate TLS, then create a realm, a client, and at least one user or federation source through the admin console. That is the "hours to days" gap, and it is real, not rhetorical.

Ongoing operational tax. This is where the free-versus-free framing misleads people. Auth.js updates are an npm update that ships with your normal deploy. Keycloak is infrastructure you own. Every Keycloak point release, and there are many across a year on the 26.x line, is a server you are responsible for patching, because an unpatched identity server is the single worst thing to leave stale. For a solo developer, that recurring maintenance is the hidden price tag on the "free" column.

When the slower-to-ship option still wins. Speed to first login is the wrong metric if your product genuinely needs what only Keycloak provides. Auth.js has no SAML 2.0 support, so an enterprise SSO requirement rules it out immediately. It has no built-in RBAC, realms, identity brokering, or LDAP and Active Directory federation, all of which Keycloak ships out of the box. If you are fronting multiple applications with one central identity layer, or you must broker logins from external OIDC and SAML providers, Keycloak's setup cost buys you capabilities you would otherwise rebuild by hand.

The decision in one line. If your auth needs are "let users sign in with Google or GitHub to my JavaScript app," Auth.js ships faster and stays cheaper to run. The moment your requirements include SAML, centralized multi-app identity, or federated directories, Keycloak's heavier setup is the faster path to a correct system, because Auth.js cannot reach the finish line at all.

When to Pick Auth.js

Auth.js is the right fit when you want authentication integrated directly into your JavaScript application with no external dependencies:

• You are building with Next.js, SvelteKit, Remix, or another supported framework.
• You want OAuth social logins with minimal configuration.
• Keeping your infrastructure simple matters more than having an enterprise feature set.
• You are comfortable writing authorization logic in your application code.
• Zero additional infrastructure is a hard requirement.

The biggest advantage is simplicity. Your auth lives in your app. There is no separate service to monitor, no Java process to babysit, and no admin console to learn. When you deploy your app, auth deploys with it.

When to Pick Keycloak

Keycloak makes sense when your authentication requirements go beyond what a library can provide:

• You are running multiple applications or microservices that need centralized auth.
• Enterprise SSO via SAML 2.0 is a hard requirement.
• You need complex role hierarchies, group-based permissions, or realm-level isolation.
• Custom authentication flows (conditional MFA, step-up auth) are part of your product.
• You are building something where the identity layer needs to be a first-class, standalone component.

If you are a solo developer building a single SaaS app and none of these apply, Keycloak is almost certainly overkill. The operational cost of running it will eat into your development time.

Verdict

Auth.js wins for solo developers in almost every typical scenario. If you are building a JavaScript web app and need authentication, Auth.js gives you a production-ready solution with zero infrastructure overhead. It supports more OAuth providers out of the box than most developers will ever need, and the community is active and growing.

Pick Keycloak only when you have a genuine enterprise requirement like SAML SSO, multi-service centralized auth, or complex RBAC that would be painful to implement in application code. For a solo developer, the time spent configuring and maintaining Keycloak would almost always be better spent building product features. Start with Auth.js. If you outgrow it, you will know exactly why, and migrating to a dedicated identity server at that point will be a well-informed decision rather than a premature one.

Sources

All figures checked on 2026-05-28.

• Auth.js providers and authentication methods (80+ providers, magic links, credentials): authjs.dev/getting-started/providers
• Auth.js framework support and recommended install (next-auth@beta): authjs.dev/getting-started/installation
• next-auth versions and publish dates (4.24.14 stable, 5.0.0-beta.31 beta): registry.npmjs.org/next-auth
• next-auth npm weekly downloads (week of 2026-05-21 to 2026-05-27): api.npmjs.org/downloads/point/last-week/next-auth
• next-auth GitHub repository (stars, primary language TypeScript): github.com/nextauthjs/next-auth
• Keycloak GitHub repository (stars, primary language Java): github.com/keycloak/keycloak
• Keycloak 26.6.2 release (latest version, released 2026-05-19): github.com/keycloak/keycloak/releases/tag/26.6.2
• Keycloak feature set (OIDC, OAuth 2.0, SAML 2.0, SSO, identity brokering, LDAP and Active Directory federation, admin console): keycloak.org