Firebase Auth vs Keycloak for Solo Developers

Quick Comparison

Firebase Auth Overview

Firebase Auth is Google's authentication service. Email/password, phone verification, anonymous auth, and social OAuth providers are all supported. The SDKs handle token generation, refresh, and session persistence automatically. Integration with Firestore security rules and Cloud Functions makes it part of a complete backend ecosystem.

The free tier covers 50,000 MAU. Mobile SDKs for iOS, Android, and Flutter handle platform-specific OAuth flows natively. Setting up Google Sign-In on a Flutter app takes minutes, not hours.

I've used Firebase Auth for mobile projects where the tight integration with Firestore made the auth-to-database pipeline seamless. Auth was working in under 30 minutes, and I moved on to building actual features.

Keycloak Overview

Keycloak is Red Hat's open-source identity and access management server. It runs as a standalone Java application and provides a comprehensive admin console for managing users, roles, clients, identity providers, and authentication flows. It supports OIDC, SAML 2.0, LDAP/AD federation, social login, MFA, and fine-grained authorization.

Keycloak is designed for organizations running multiple applications that need unified authentication. Deploy Keycloak, configure your apps as clients, and users authenticate once for access to all applications. The admin console handles user management, role assignment, and policy configuration.

I deployed Keycloak for a multi-app project that needed SSO. The OIDC integration worked reliably, and the admin console was useful for managing users. But the deployment itself, configuring the Java server, setting up the database, handling TLS, consumed a full weekend.

Key Differences

Setup complexity. Firebase Auth takes 20-30 minutes. Install the SDK, configure providers in the Firebase console, call auth methods. Keycloak takes a weekend. Deploy the Java server, configure PostgreSQL, set up TLS, create realms and clients, configure providers. The complexity gap is enormous.

Managed vs self-hosted. Firebase Auth is fully managed by Google. Uptime, security patches, scaling, and infrastructure are their responsibility. Keycloak runs on your server. You handle deployments, updates, database backups, memory tuning, and monitoring. For a solo developer, the operational burden of Keycloak is significant.

SSO capability. Keycloak's primary strength is SSO across multiple applications. Configure each app as a client, and users log in once for access to all of them. Firebase Auth authenticates users for Firebase projects. Cross-application SSO isn't its design goal. If you need unified login across multiple apps, Keycloak handles it natively.

Enterprise features. Keycloak provides SAML 2.0 support, LDAP/Active Directory federation, fine-grained authorization, and custom authentication flows. Firebase Auth has none of these. If your project requires SAML SSO for enterprise clients or LDAP integration with an existing directory, Keycloak is the only option here.

Resource requirements. Firebase Auth consumes nothing on your infrastructure. It's a cloud service. Keycloak needs at minimum 512MB-1GB RAM for the Java server plus a PostgreSQL database. On a small VPS shared with your application, Keycloak's memory footprint is noticeable.

Mobile support. Firebase has native SDKs for iOS, Android, Flutter, and Unity. Keycloak doesn't have mobile SDKs. Mobile apps authenticate against Keycloak using standard OIDC flows, which works but requires more code than Firebase's native integration.

By the Numbers (2026)

Here is where the two products actually stand as of late May 2026, with the figures pulled from official pricing pages, the GitHub repository, and the npm registry.

Firebase Auth

• Client SDK: the firebase npm package sits at version 12.14.0, published under the Apache-2.0 license.
• Reach: roughly 7.25 million npm downloads in a single week (week of 2026-05-21), which tells you how broadly the SDK is deployed.
• Free tier: 50,000 monthly active users at no cost for email/password and social sign-in.
• Paid tier above the free band, billed through Google Cloud Identity Platform per monthly active user: $0.0055 for 50,001 to 100,000 MAU, $0.0046 for 100,001 to 1,000,000 MAU, $0.0032 for 1,000,001 to 10,000,000 MAU, and $0.0025 beyond that.
• Enterprise SSO (SAML 2.0 and OIDC federation) is a separate Identity Platform line, free for only the first 50 MAU, then $0.015 per MAU.
• Phone and SMS authentication is billed per message, not per MAU, and ranges from about $0.01 in the US, Canada, and India up to $0.06 or more in many other regions.

Keycloak

• Latest release: 26.6.2, shipped 2026-05-19, on the heels of the 26.6.0 feature release.
• Project momentum: more than 34,600 stars and 8,400 forks on GitHub, with the codebase written in Java.
• License cost: zero. It is open source under Apache-2.0, so the only money you spend is on the server and database that run it.
• Runtime: the official server container runs on OpenJDK 21, and the server needs a relational database (PostgreSQL, MySQL, MariaDB, and others are supported) plus, in practice, at least 512MB to 1GB of RAM.
• Protocol coverage in the current line: OIDC and OAuth 2.0 (including DPoP), SAML 2.0 with step-up auth, LDAP and Active Directory federation, MFA, fine-grained authorization, and the Organizations feature for multi-tenant setups. The 26.6 line also added zero-downtime patch updates and a Workflows engine for automating realm administration.

The headline contrast is that Firebase charges you nothing until you cross 50,000 active users, while Keycloak charges you nothing in license fees ever but bills you in server cost and operational time from day one.

Real Cost at Solo-Dev Scale

Pricing pages are abstract until you plug in a real workload, so here is a concrete scenario for a solo developer.

Assumptions. A consumer web and mobile app with 8,000 monthly active users, email/password plus Google and Apple social sign-in, no SMS or phone verification, and no SAML or enterprise SSO. This is a typical early-stage indie product that has found some traction but is nowhere near scale.

Firebase Auth. Eight thousand MAU is comfortably under the 50,000 free threshold, and there is no SMS in this workload, so the authentication bill is exactly $0 per month. You would only start paying once you cross 50,000 active users, and even then the first paid band is $0.0055 per MAU. To put that in perspective, going from 50,000 to 60,000 MAU adds 10,000 paid users at $0.0055 each, which is $55 per month. Firebase Auth stays free for the entire life of most solo projects.

Keycloak. The software license is free, but you have to run it. A small managed VPS sized to hold a 512MB to 1GB Java process plus a PostgreSQL database realistically lands around $12 to $24 per month on common providers, and that node has to stay up whether you have 8 users or 8,000. So the floor is roughly $12 to $24 per month, every month, regardless of how few users authenticate, plus your own time spent on patches, backups, and TLS renewal.

The verdict on cost. For this workload Firebase Auth is free and Keycloak is not. Keycloak only becomes the cheaper option in raw dollars once your Firebase MAU bill climbs past your hosting bill, and at $0.0055 per MAU that crossover sits well into six-figure user counts. For a solo developer running a normal-sized app, the dollars favor Firebase, and the time spent favors it even more.

When to Choose Firebase Auth

• You're building a consumer-facing app (web or mobile)
• You want auth working in under 30 minutes
• You're using Firebase for your backend
• Mobile-first development with native SDK support matters
• You don't need SSO across multiple separate applications

When to Choose Keycloak

• You need SSO across multiple applications
• SAML 2.0 or LDAP/AD integration is required
• You want a full admin console for user and role management
• You're comfortable managing Java application servers
• Enterprise identity management features are a real requirement

The Verdict

For the vast majority of solo developers, Firebase Auth is the right choice. It's simple, free at meaningful scale, and handles consumer auth perfectly. You'll have authentication working in minutes instead of days, and you can focus on building your product instead of managing identity infrastructure.

Keycloak is the right choice when you have a specific enterprise need: SSO across multiple apps, SAML integration, or LDAP federation. These aren't features you'll need for a typical solo project. They're features you need when your users are enterprises with existing identity infrastructure.

My recommendation: don't use Keycloak unless you have a concrete requirement that only Keycloak (or a similar identity server) can satisfy. For everything else, Firebase Auth gets you to working auth faster, costs nothing to operate, and lets you focus on what actually makes your product valuable. If enterprise needs arise later, you can add Keycloak alongside Firebase Auth for those specific flows.

Sources

All figures checked on 2026-05-28.

• Google Cloud Identity Platform pricing (per-MAU tiers): https://cloud.google.com/identity-platform/pricing
• Firebase pricing (50,000 MAU free tier, SAML/OIDC enterprise tier): https://firebase.google.com/pricing
• Firebase Authentication documentation: https://firebase.google.com/docs/auth
• Firebase Auth cost breakdown and SMS rates: https://www.metacto.com/blogs/the-complete-guide-to-firebase-auth-costs-setup-integration-and-maintenance
• firebase npm package latest version: https://registry.npmjs.org/firebase/latest
• firebase npm weekly downloads: https://api.npmjs.org/downloads/point/last-week/firebase
• Keycloak GitHub repository (stars, forks, language): https://github.com/keycloak/keycloak
• Keycloak 26.6.2 release: https://github.com/keycloak/keycloak/releases/tag/26.6.2
• Keycloak 26.6.0 feature release notes: https://www.keycloak.org/2026/04/keycloak-2660-released
• Keycloak release notes (protocols, JDK requirement): https://www.keycloak.org/docs/latest/release_notes/index.html