Keycloak vs. Auth0: The Open-Source Alternative (2026 Guide)
Keycloak vs. Auth0: Choosing an Open-Source Alternative for Authentication
Last updated: 2026 — pricing and feature comparisons reflect Auth0's current published plans.
When it comes to implementing authentication and authorization in web applications, Auth0 and Keycloak are two prominent solutions that offer robust security features. Auth0 is a popular, fully managed cloud platform; Keycloak is an open-source alternative that competes strongly on cost, control, and flexibility. This post compares the two across cost of ownership, architecture and deployment, maintenance, functionality, and support — and explains why pairing Keycloak with a managed host like Phase Two often gives you the best of both.
A quick note before we start: much of the older commentary about Keycloak's limitations is out of date. Many critiques still circulating online cite G2 reviews that are four-plus years old — more than ten major Keycloak versions behind the current release. When researching Keycloak, check which version is being discussed. We keep the information below aligned with recent Keycloak versions.
If you're weighing other vendors too, we maintain open-source-alternative comparisons for Okta, WorkOS, Ping Identity, FrontEgg, and OneLogin — and a broader overview of Keycloak as an open-source alternative to Auth0, WorkOS, Okta, and Cognito.
Keycloak vs. Auth0 at a Glance
| Dimension | Auth0 | Keycloak (with Phase Two) |
|---|---|---|
| Licensing model | Proprietary, subscription | Open source (Apache 2.0), no license fee |
| Pricing driver | Per monthly active user (MAU) + features | Fixed infrastructure / hosting cost, not per-user |
| Cost predictability | Scales with users and features | Predictable; decoupled from user growth |
| Deployment | Cloud SaaS only | Self-hosted, your cloud, on-premise, or managed |
| Data residency / sovereignty | Limited control | Full control over environment and data location |
| Maintenance | Fully managed by Auth0 | Managed by you, or by Phase Two if hosted |
| Standards | OAuth 2.0, OIDC, SAML | OAuth 2.0, OIDC, SAML |
| Extensibility | Actions framework (bounded) | Full source access + SPIs/extensions |
| Vendor lock-in | High | Low — portable, standards-based |
| Best fit | Teams wanting zero-ops and paying per user | Teams wanting control, predictable cost, or on-prem |
Cost of Ownership
Total cost of ownership has many factors. We've written extensively about choosing an open-source IAM over a managed proprietary service.
Auth0: Auth0 operates on a subscription model that can be appealing for startups or small projects with minimal authentication needs. Its free tier is generous on paper — up to 25,000 monthly active users (MAU) — but it's bounded on connections, organizations, and features, and most production workloads quickly outgrow it.
Here's the catch: Auth0's list prices look modest until you map them to how a real application actually uses the platform. As of 2026, Auth0's published pricing (per month, billed monthly) scales like this:
| Monthly active users | B2C Essentials | B2C Professional | B2B Essentials |
|---|---|---|---|
| 1,000 | $70 | $240 | $300 |
| 5,000 | $350 | $1,000 | $1,300 |
| 10,000 | $700 | $1,600 | $2,100 |
| 20,000 | $1,400 | $3,200 | $3,800 |
Figures reflect Auth0's published list pricing as of 2026 (auth0.com/pricing); Auth0 changes pricing periodically, so confirm current rates for your tier and region.
Two things push the real bill well beyond the headline numbers:
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The features you actually need live in higher tiers and add-ons. SAML, LDAP/Active Directory federation, log streaming, and similar capabilities move you up a band — and several common needs are billed as separate line items on top of your subscription. Additional enterprise SSO connections run about $100/month each on B2B plans; MFA is a $100/month add-on on B2B Essentials; machine-to-machine (M2M) tokens are metered separately (up to roughly $1,200/month for 300,000 tokens); and the newer AI Agents add-on is priced at 50% of your base subscription. Every capability you switch on either bumps your tier or tacks on a charge.
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"Users" and "organizations" aren't cheap. If you sell to businesses, Auth0's B2B model is the one that fits — and it costs materially more than B2C at the same scale (for example, $3,800/month for B2B Essentials vs. $1,400/month for B2C Essentials at 20,000 MAU). Note also that "users" can mean people or devices, and organizations, enterprise connections, and per-customer SSO all push the number up.
For anything beyond mid-size, Auth0 routes you into a custom Enterprise contract. In practice those negotiations tend to land in the six figures annually — we routinely talk to teams whose Auth0 quotes target $100K+ per year once SSO, MFA, organizations, and log streaming are bundled in. The problem isn't that any single number is outrageous; it's that the total is hard to predict and climbs with every feature and every user you add.
Keycloak: Keycloak is an open-source solution originally developed and backed by Red Hat. It is free to use regardless of the number of users or scale of the project, which makes it attractive for teams looking to control costs or avoid vendor-specific pricing. The primary cost is hosting and operating the software — server costs plus setup and maintenance overhead — which means your spend tends to be fixed, driven by infrastructure rather than by user counts or feature gates.
Winner: Keycloak. Phase Two's managed hosting offers a capable free tier to test and integrate authentication, and as your application's needs grow, Keycloak remains far more cost-effective. See a side-by-side pricing estimate vs. Auth0.
Architecture and Deployment
Auth0: Auth0 is a cloud-based service, so there's little infrastructure to set up or configure. That enables quick deployment and removes much of the DevOps burden. The trade-off: enterprises with strict regulatory or data-residency requirements often need on-premise options that a SaaS-only model can't provide.
Keycloak: Keycloak can be deployed on-premise, in your own cloud, or via a managed cloud service. Because you control the deployment environment, it conforms to compliance and data-sovereignty needs. Initial infrastructure setup can take more effort, but the result is a flexible, standards-based system that integrates cleanly with your applications.
Winner: Depends. If you need on-premise or strict data control, Keycloak wins clearly. For a purely hosted option, either can work — and Keycloak still gives you the flexibility to self-host or use managed hosting.
Maintenance
Auth0: As a managed service, Auth0 requires minimal maintenance from your side. Auth0 handles updates, security patches, and infrastructure, keeping the system current.
Keycloak: Self-hosted Keycloak requires more attention — installation, configuration, upgrades, and the underlying infrastructure. For teams without that expertise or capacity, this is a real consideration. The upside is greater control over deployment and security posture, which matters in regulated environments. Phase Two removes this trade-off entirely: with managed hosting and zero-downtime upgrades, you get Keycloak's control without the operational load.
Winner: Auth0 (for self-hosted Keycloak); a tie when Keycloak is managed by Phase Two.
Functionality and Flexibility
Auth0: Auth0 offers a broad set of authentication features out of the box — social logins, enterprise federation, database connections, and more — and supports OAuth 2.0, OpenID Connect, and SAML. It also provides analytics and monitoring. Customization happens through its Actions framework, which can become difficult to manage as logic grows outside the main application.
Keycloak: Keycloak matches Auth0 on core functionality, supporting the same protocols and user federation, with customizable login, registration, and account-management UIs. Being open source, it lets developers extend the codebase and integrate with other systems far more freely — a higher ceiling for customization in exchange for some additional developer effort. A standout capability is Keycloak's on-premise deployment options; if your requirements include on-prem, learn how Keycloak handles user management and identity brokering for on-premise apps.
Winner: Keycloak. The two are comparable on features, but Keycloak is far more extensible and configurable, and can grow with your application.
Migrating from Auth0 to Keycloak
Moving off Auth0 is more approachable than many teams expect. Keycloak imports users, supports gradual cutover, and brokers identities so you can transition without disrupting access. We've built tooling and a process specifically for this — see Migrate to Keycloak for how we move teams off Auth0, Okta, and Cognito.
You can also run Keycloak alongside Auth0 during a transition: Keycloak can act as a broker that delegates authentication to an external IdP such as Auth0. That lets you keep existing Auth0 connections while Keycloak handles internal permissions, roles, and a consistent login experience — a low-risk path to migrating one piece at a time.
Which One Is Best for Me?
Choosing between Auth0 and Keycloak depends on your organization's needs and capabilities. Auth0 is an excellent fit for teams that want a fully managed solution and are comfortable with costs tied to user counts and features. For teams that prioritize cost predictability, need infrastructure control or on-premise deployment, or want extensive customization, Keycloak is a powerful, budget-friendly alternative. Both offer strong documentation and community support.
Ultimately, we believe the strongest setup marries the two ideas: Keycloak's openness and flexibility with the convenience of a managed service. Phase Two offers hosting options that fit businesses of many sizes, so you get Keycloak's control and fixed, predictable costs without taking on the operational burden yourself.
Ready to compare for your own usage? Estimate your cost vs. Auth0 or try a free deployment.
Frequently Asked Questions
Is Keycloak a good alternative to Auth0? Yes. Keycloak supports the same core standards as Auth0 (OAuth 2.0, OpenID Connect, SAML) and matches it on most authentication and authorization features, while being open source and free of per-user licensing. The main trade-off is operational overhead, which a managed host like Phase Two removes.
Is Keycloak cheaper than Auth0? For most growing applications, yes. Auth0 pricing scales with monthly active users and feature tiers, while Keycloak's cost is driven by hosting infrastructure and stays largely fixed as your user base grows. Teams moving from Auth0 to managed Keycloak frequently see substantial savings.
Can I migrate from Auth0 to Keycloak? Yes. Keycloak can import your users and broker authentication to Auth0 during a phased cutover, so you can migrate incrementally without disrupting users. See Migrate to Keycloak.
Does Keycloak support SAML, OIDC, and OAuth 2.0? Yes. Keycloak is built on these standards and interoperates with both modern applications and legacy systems, including LDAP and Active Directory.
Can Keycloak be self-hosted or run on-premise? Yes. Keycloak can run on-premise, in your own cloud, or as a managed service. This flexibility is a key advantage over Auth0's cloud-only model, especially for data-residency and compliance requirements.