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.

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.