Choosing the right IAM (identity and access management) tool for your SaaS product can be tricky.
With so many options promising developer-friendly integration, enterprise single sign-on (SSO), and secure user management, it’s easy to get lost in the features.
To help you cut through the noise, we’ve scored four leading IAM solutions — Auth0, Keycloak, Clerk, and FusionAuth — across 7 essential criteria for SaaS platforms, including developer experience, tenant architecture, and enterprise readiness.
We’ve prepared a handy graphic for quick comparison with more detailed discussion below. Enjoy!
Hosting flexibility & control
IAM tools vary in where and how they can be deployed — something that can be crucial when dealing with compliance, infrastructure preferences, or scaling strategy.
Keycloak
Keycloak is the most flexible in terms of hosting. It’s open-source, self-hosted, and can run anywhere — in the cloud/as a containerised app or on-premises. Ideal for teams that want full control over their environment.
Score: 4
FusionAuth
FusionAuth also offers both cloud and self-hosted options. You can deploy it in Docker, Kubernetes, or as a managed service. Slightly behind Keycloak due to its flexibility coming at a price.
Score: 3
Auth0
Auth0 is primarily a cloud platform, with enterprise-only self-hosting options via Okta. For most teams, it’s “cloud or nothing,” which limits flexibility.
Score: 2
Clerk
Clerk is entirely cloud-hosted, with no option for self-hosting. While this makes it easy to get started, it limits control.
Score: 1
Custom auth flows & UI control
Customising how users log in and how the UI looks is key to user experience and brand consistency — and often to meeting specific auth logic requirements.
Keycloak
Keycloak offers the deepest customisation, from login themes and user flows to full control over protocols and behaviour. It’s a developer’s playground, assuming you’re comfortable getting your hands dirty.
Score: 4
Auth0
Auth0 has strong extensibility via hooks, Actions, and embedded flows. While the hosted login page has some limits, it’s flexible enough for most SaaS use cases.
Score: 3
FusionAuth
FusionAuth provides good theming, email templates, and event hooks, but lacks some of the low-level control you get with Keycloak or the modern polish of Clerk.
Score: 2
Clerk
Clerk gives you sleek, modern pre-built components and a great out-of-the-box developer experience. However, customisation beyond visual styling is limited — you can’t significantly alter flows or inject logic into the authentication process. While the polish is there, the lack of deep extensibility means it ranks lowest for control.
Score: 1
SaaS-ready tenant architecture
For B2B SaaS, tenant modelling and organisational access control is a core requirement, not an afterthought.
Auth0
Auth0 leads the way here with built-in support for organisations, metadata, role-based access control, and per-tenant configuration. It’s clearly designed for SaaS at scale.
Score: 4
Clerk
Clerk also shines in this area, offering out-of-the-box multi-tenancy, org-based access control, and scoped user roles — all baked into the developer experience.
Score: 4
Keycloak
Keycloak supports tenant isolation through manual configuration and “realms,” but lacks SaaS-specific features like org metadata or easy per-tenant RBAC.
Score: 2
FusionAuth
FusionAuth supports tenants and role separation, but lacks some of the more opinionated structures that make SaaS development faster and simpler.
Score: 1
Enterprise SSO support
Enterprise SSO is essential for working with large customers who need to bring their own identity provider.
Auth0
Auth0 supports everything: SAML, OIDC, SCIM, and prebuilt integrations for major IdPs like Okta, Google Workspace, and Azure AD.
Score: 4
Keycloak
Keycloak is protocol-complete. It can handle SAML, OIDC, brokering, but it requires more setup and maintenance than Auth0.
Score: 3
FusionAuth
FusionAuth supports the necessary protocols (SAML, OIDC) and allows custom configuration, but doesn’t provide the full suite of enterprise-level tooling.
Score: 2
Clerk
Clerk offers support for SAML and OIDC, but only on higher pricing tiers, and lacks the depth and integrations of the others.
Score: 1
Developer UX & tooling maturity
A tool’s success often depends on how fast and smoothly developers can use it to ship production-ready auth.
Clerk
Clerk delivers the most polished experience: modern APIs, React components, CLI tools, and fast integration workflows. It’s made for speed.
Score: 4
Auth0
Auth0 has great SDKs, clear documentation, and strong tooling, but it’s showing its age in some places. Still excellent, just not the slickest.
Score: 3
FusionAuth
FusionAuth is developer-friendly with clean REST APIs and helpful docs. It’s not quite as polished as Clerk or Auth0 but still solid.
Score: 3
Keycloak
Keycloak is powerful but infrastructure-heavy. The DX is steep, with a need for manual config, limited tooling, and fewer onboarding niceties.
Score: 1
Pricing transparency & scalability
Cost structure and predictability matter — especially when you’re scaling and need to avoid nasty surprises.
Keycloak
Keycloak is entirely free and open-source. No licence fees, no user limits. You only pay for infrastructure.
Score: 4
FusionAuth
FusionAuth offers a generous free tier and affordable paid plans. Self-hosting is free; cloud pricing is flat and clear.
Score: 3
Clerk
Clerk offers predictable pricing with a free tier and usage-based billing. It’s straightforward but not as flexible as FusionAuth.
Score: 2
Auth0
Auth0 starts free, but the cost grows quickly. Pricing complexity and gated features make it hard to forecast spend at scale.
Score: 1
Support ecosystem & community
Documentation, community size, and access to support all affect how fast you can solve problems and grow.
Auth0
Auth0 has been around for years and is backed by Okta. You’ll find extensive docs, examples, forums, and commercial support.
Score: 4
FusionAuth
FusionAuth has excellent documentation, active forums, and optional paid support. It strikes a good balance between commercial and community.
Score: 4
Keycloak
Keycloak has an active open-source community and is backed by Red Hat. Docs are decent but community support is inconsistent.
Score: 2
Clerk
Clerk has an engaged and responsive team, with good documentation and a growing Discord community — but it’s still small.
Score: 2
How we can help
Whether you’re a startup hoping to build a unicorn or an established product team about to switch auth provider, your IAMs tool is a key decision; it doesn’t just enable user sign-up and login. It lays the foundation for secure and seamless access across your stack.
The security features and other attributes of the tool you choose will allow you to protect sensitive data, control service account access and ultimately form a substantial part of your security posture.
At Just After Midnight, we’ve helped global SaaS products stay secure, scale and keep serving customers through our unique 24/7 support service for SaaS businesses and cloud-native expertise.
To find out how we could help you, just get in touch.
