Keycloak vs FusionAuth: Open Source Identity Platform Comparison

Last updated: March 2026

Choosing an identity platform is a long-term architectural decision. Both Keycloak and FusionAuth position themselves as developer-friendly identity solutions, but they differ significantly in licensing, extensibility, community size, and operational model. This comparison examines both platforms across the dimensions that matter most for engineering teams evaluating their options.

Licensing: Truly Open Source vs. Source-Available

This is the most important distinction between the two platforms.

Keycloak is licensed under the Apache License 2.0, one of the most permissive open-source licenses. You can use, modify, distribute, and sell Keycloak without restriction. There is no “community edition” vs. “enterprise edition” split — every feature is available to everyone.

FusionAuth uses a dual-licensing model. The “Community” edition is source-available but not open source in the OSI-approved sense. Key features — including advanced MFA, SCIM provisioning, entity management, advanced threat detection, and breached password detection — are locked behind paid plans. FusionAuth’s licensing terms restrict redistribution and competing offerings.

Aspect	Keycloak	FusionAuth
License	Apache 2.0 (OSI-approved)	Proprietary + source-available
All features free	Yes	No (gated tiers)
Redistribution	Unrestricted	Restricted
Modification rights	Full	Limited
Competing product clause	None	Yes

For organizations that need the flexibility of true open source — whether for compliance, audit, or freedom to customize — Keycloak is the clear choice.

Feature Comparison

Both platforms cover the core identity and access management features. The differences emerge in advanced capabilities and how they are packaged.

Authentication

Feature	Keycloak	FusionAuth
Username/Password	Yes	Yes
Social Login	Yes (20+ providers built-in)	Yes (10+ providers)
Passwordless (WebAuthn/Passkeys)	Yes	Yes (paid plans)
OTP (TOTP/HOTP)	Yes	Yes
SMS/Email OTP	Yes (via extensions)	Yes (paid plans)
Step-Up Authentication	Yes (ACR/LoA)	Limited
Conditional MFA	Yes (via authentication flows)	Yes (paid plans)
Kerberos/SPNEGO	Yes	No
X.509 Client Certificates	Yes	No
Device Authorization Grant	Yes	Yes

Keycloak includes all authentication methods in the base distribution. FusionAuth gates several MFA methods and advanced authentication features behind paid plans. For more on Keycloak’s MFA capabilities, see Multi-Factor Authentication.

Identity Federation

Feature	Keycloak	FusionAuth
OIDC Identity Brokering	Yes	Yes
SAML Identity Brokering	Yes (SP and IdP)	Yes
LDAP/Active Directory	Yes (built-in)	Yes (via LDAP connector)
Social Identity Providers	Yes (Google, GitHub, Facebook, etc.)	Yes
Account Linking	Yes (automatic and manual)	Yes
First Login Flow Customization	Yes (detailed flow builder)	Limited

Both platforms handle identity federation well. Keycloak’s advantage is its highly configurable first-login flow, which lets you define exactly how brokered identities are linked, what attributes are mapped, and whether additional verification is required. See Identity Providers for more.

Authorization

Feature	Keycloak	FusionAuth
RBAC	Yes	Yes
Fine-Grained Authorization (UMA)	Yes	No
Resource-Based Permissions	Yes (Authorization Services)	No
Policy Evaluation	Yes (JavaScript, role, time, etc.)	No
Group-Based Access	Yes	Yes
Application-Level Roles	Yes (client roles)	Yes (application roles)

Keycloak’s authorization services are significantly more powerful. The built-in policy engine supports UMA 2.0, resource servers, and multiple policy types. FusionAuth relies on application-side authorization logic using roles and groups. For a deep dive into Keycloak’s authorization model, see our post on fine-grained authorization in Keycloak and the RBAC feature page.

User Management

Feature	Keycloak	FusionAuth
Admin Console	Yes (web-based)	Yes (web-based)
Admin REST API	Yes (comprehensive)	Yes (comprehensive)
User Self-Registration	Yes	Yes
Custom User Attributes	Yes	Yes
User Federation (LDAP/AD)	Yes (sync + proxy modes)	Yes
SCIM 2.0 Provisioning	Yes (via extensions)	Yes (paid plans)
User Import/Export	Yes (JSON)	Yes (JSON/CSV)

Both platforms provide solid user management. FusionAuth’s admin console has a more modern visual design out of the box, while Keycloak’s admin console (completely rewritten in Keycloak 22+) focuses on functional depth. For SCIM provisioning, see the SCIM feature page and test your SCIM implementation with the SCIM Endpoint Tester.

Extensibility

This is where the platforms diverge most significantly.

Keycloak: Service Provider Interface (SPI)

Keycloak’s extensibility is built on Java SPIs. You can replace or extend almost any component:

• Authenticator SPI: Build custom authentication steps (hardware token integration, custom challenge/response).
• Event Listener SPI: React to authentication events (send to SIEM, trigger webhooks).
• User Storage SPI: Federate users from any custom data source.
• Protocol Mapper SPI: Add custom claims to tokens.
• Theme SPI: Fully customize login pages, email templates, and the admin console.
• REST Resource SPI: Add custom REST endpoints to Keycloak.

Example custom authenticator:

public class CustomStepUpAuthenticator implements Authenticator {

    @Override
    public void authenticate(AuthenticationFlowContext context) {
        // Custom logic to determine if step-up is needed
        String acr = context.getAuthenticationSession()
            .getClientNote("requested_acr");

        if ("2".equals(acr) && !hasCompletedMfa(context)) {
            context.challenge(
                context.form().createForm("custom-mfa.ftl")
            );
        } else {
            context.success();
        }
    }

    @Override
    public void action(AuthenticationFlowContext context) {
        String otpCode = context.getHttpRequest()
            .getDecodedFormParameters().getFirst("otp");

        if (validateOtp(context, otpCode)) {
            context.success();
        } else {
            context.failureChallenge(
                AuthenticationFlowError.INVALID_CREDENTIALS,
                context.form().setError("Invalid OTP").createForm("custom-mfa.ftl")
            );
        }
    }
}

The SPI model gives you deep control over Keycloak’s behavior without forking the codebase. Extensions are deployed as JAR files into the providers directory.

FusionAuth: Lambdas

FusionAuth uses “Lambdas” (server-side JavaScript functions) for customization. Lambdas can modify:

• JWT population (adding custom claims)
• SAML assertion population
• OpenID Connect reconciliation (mapping external IdP data)
• Self-service registration validation

Lambdas are simpler to write but more limited in scope. You cannot build custom authentication flows, add new protocol support, or replace core components. For use cases that exceed Lambda capabilities, FusionAuth offers webhooks to call external services.

Comparison

Extensibility Aspect	Keycloak	FusionAuth
Custom authentication flows	Yes (SPI)	No
Custom token claims	Yes (Protocol Mapper SPI)	Yes (Lambdas)
Custom user storage	Yes (User Storage SPI)	No
Custom event handling	Yes (Event Listener SPI)	Yes (webhooks)
Custom REST endpoints	Yes (REST Resource SPI)	No
Login page theming	Yes (FreeMarker templates)	Yes (themes/templates)
Email template customization	Yes	Yes
Plugin deployment	JAR files (hot deploy)	N/A

For teams that need deep customization — especially custom authentication flows or custom user storage backends — Keycloak’s SPI architecture is substantially more capable.

Community and Ecosystem

Keycloak:

• GitHub: 25,000+ stars (as of March 2026)
• Backed by Red Hat (IBM), with commercial support available via Red Hat Build of Keycloak (RHBK)
• Active contributor community with hundreds of contributors
• CNCF incubating project
• Extensive third-party extensions, Terraform providers, Helm charts, and Kubernetes operators
• Large Stack Overflow community (12,000+ questions)

FusionAuth:

• GitHub: 1,500+ stars
• Backed by FusionAuth, Inc. (venture-funded)
• Smaller contributor community (source-available limits external contributions)
• Growing ecosystem of SDKs and integrations
• Active community forums and Discord

The ecosystem difference is meaningful. Keycloak’s large community means more extensions, more battle-tested configurations, and more answers to common questions. The Terraform provider for Keycloak, for instance, is mature and widely used, while FusionAuth’s Terraform support is more recent.

Deployment and Operations

Keycloak

Keycloak runs as a Java application (Quarkus-based since Keycloak 17). Deployment options:

• Docker: Official images on quay.io/keycloak/keycloak
• Kubernetes: Keycloak Operator for automated deployment and management
• Bare metal/VM: Standard Java application with systemd service
• Managed hosting: Available through providers like Skycloak

Keycloak supports external databases (PostgreSQL, MySQL, MariaDB, Oracle, MSSQL) and includes Infinispan for distributed caching and session replication.

Use our Keycloak Docker Compose Generator to create a development setup, or the Keycloak Config Generator for custom configurations.

FusionAuth

FusionAuth runs as a Java application with Elasticsearch for search. Deployment options:

• Docker: Official Docker images
• Kubernetes: Community Helm charts
• Bare metal/VM: Debian/RPM packages
• FusionAuth Cloud: Managed hosting by FusionAuth

FusionAuth requires Elasticsearch (or OpenSearch) in addition to the database, adding operational complexity compared to Keycloak’s simpler architecture.

Operations Aspect	Keycloak	FusionAuth
Database support	PostgreSQL, MySQL, MariaDB, Oracle, MSSQL	PostgreSQL, MySQL
Search dependency	None (built-in)	Elasticsearch required
Clustering	Built-in (Infinispan)	Built-in
Kubernetes Operator	Official	Community
Configuration as code	Terraform provider, Admin API	Terraform provider, Admin API
Backup/Restore	Database-level	Database + Elasticsearch

Pricing Comparison

Keycloak: Free. All features. Forever. The only costs are infrastructure and operational effort (or a managed hosting fee).

FusionAuth (as of March 2026):

• Community: Free, but limited features. No advanced MFA, no SCIM, no breached password detection, no advanced threat detection.
• Starter: Paid per monthly active user. Adds some advanced features.
• Essentials: Higher per-user pricing. Adds SCIM, advanced MFA, entity management.
• Enterprise: Custom pricing. Adds all features plus premium support.

For a cost comparison of different identity solutions, see our IAM solutions ROI comparison and use the ROI Calculator to estimate your costs.

When to Choose Keycloak

Choose Keycloak when:

• Open source matters: You need Apache 2.0 licensing for compliance, audit, or redistribution.
• Deep customization is required: Custom authentication flows, user storage federation, or protocol extensions via SPIs.
• Standards compliance is critical: Full OIDC, SAML, UMA 2.0, and FAPI support.
• Community and ecosystem: You want access to the largest open-source identity community and ecosystem.
• No vendor lock-in: You want the freedom to self-host, use any managed provider, or switch between them.
• Fine-grained authorization: You need built-in policy-based authorization (UMA, resource servers).

When to Consider FusionAuth

Consider FusionAuth when:

• Developer experience is the top priority: FusionAuth’s documentation and getting-started experience is polished.
• You prefer a commercial support model: FusionAuth offers integrated commercial support.
• You do not need deep customization: Lambdas and webhooks cover your extension needs.
• You are comfortable with source-available licensing: The licensing restrictions do not affect your use case.

Migration Path

If you are evaluating a switch from FusionAuth to Keycloak (or vice versa), the key migration considerations are:

• User data: Both platforms support JSON-based user export/import. Password hashes may require re-hashing depending on the algorithm used.
• Application configuration: OIDC client configurations are similar. SAML configurations will need manual recreation.
• Customizations: FusionAuth Lambdas will need to be rewritten as Keycloak protocol mappers or SPIs.
• Integrations: Both platforms support standard protocols, so downstream applications should need minimal changes.

For identity brokering between the two during migration, see our guide on Keycloak identity brokering with FusionAuth.

Wrapping Up

Keycloak and FusionAuth serve similar purposes but differ fundamentally in philosophy. Keycloak is a true open-source project backed by a large community with enterprise-grade features available to everyone. FusionAuth is a commercial product with a source-available community tier.

For teams that value open-source licensing, deep extensibility through SPIs, and access to a large community, Keycloak is the stronger choice. Its standards compliance, authorization services, and battle-tested production track record make it the go-to platform for serious identity infrastructure.

If you want the power of Keycloak without the operational overhead of self-hosting, Skycloak provides fully managed Keycloak hosting with automated upgrades, backups, and enterprise SLAs. Check out pricing to find the right plan for your team.