#1★ TOP PICK
Keycloak
The mature, CNCF-backed open-source identity and access management server.
90
OPEN SOURCEApache-2.0SELF-HOSTLOCAL-FIRST
Keycloak is a full-featured IAM server originally built by Red Bull's security team and now a CNCF Incubating project. It supports OIDC, OAuth2, and SAML, social and enterprise identity brokering, fine-grained authorization, and a built-in admin console, and it's the most widely deployed self-hosted alternative to Auth0/Okta in production today.
Strengths
- +Apache-2.0, fully open-source, no feature gating between a 'community' and 'enterprise' edition
- +Extremely mature — 10+ years in production at large scale, CNCF Incubating project with active governance
- +Broad protocol support (OIDC, SAML, OAuth2) and identity brokering to external IdPs out of the box
- +Large ecosystem of themes, extensions, and Kubernetes operators for production deployment
Trade-offs
- −Runs on the JVM — heavier resource footprint than lightweight Go-based alternatives, and the admin console/config model has a real learning curve
- −You own uptime, patching, and database backups for something security-critical — a genuine operational responsibility Auth0 absorbs for you
- −Theming the login UI to match a product's brand takes more custom work than Auth0's Universal Login customization
Free / self-host (Docker image or standalone distribution); commercial support available via Red Hat build of Keycloak (RHBK) for enterprises that want a support contract. #2
authentik
A modern, self-hostable identity provider with a flexible visual flow builder.
85
OPEN SOURCEMIT (core); authentik/enterprise/ subdirectory carries its own separate license for paid enterprise featuresSELF-HOSTLOCAL-FIRST
authentik is a self-hosted identity provider built around a visual 'flow' system that lets you customize login, enrollment, and recovery steps without deep protocol expertise. It supports OIDC, SAML, LDAP, SCIM, and social login, and ships as a straightforward Docker Compose or Helm deployment aimed at teams who want Keycloak-class capability with a friendlier setup experience.
Strengths
- +Genuinely MIT-licensed for the core product — no AGPL copyleft concerns for embedding or forking
- +Visual flow builder makes multi-step login/enrollment/recovery customization far more approachable than editing raw protocol config
- +Good out-of-box support for LDAP and SCIM alongside OIDC/SAML, useful for bridging older enterprise directories
- +Active, fast-moving project with frequent releases
Trade-offs
- −The enterprise/ directory ships under authentik's own separate license, not MIT — some advanced features are gated behind the paid tier even when self-hosting the core
- −Younger and smaller community than Keycloak, so fewer third-party guides and Stack Overflow answers exist for edge cases
- −Flow builder flexibility means misconfiguration is possible; production hardening still requires real identity-ops knowledge
Free / self-host for the core MIT-licensed product; a hosted 'authentik Security' cloud offering and an Enterprise tier (support SLA, extra features under the separate enterprise/ license) are available paid. #3
Ory Kratos
A headless, API-only identity server for teams that want to build their own login UI.
84
OPEN SOURCEApache-2.0SELF-HOSTLOCAL-FIRST
Ory Kratos is a headless identity and user-management server — it handles registration, login, MFA, account recovery, and profile management entirely through APIs, with no bundled UI. It's designed for teams who want full control over the login experience and are comfortable building their own frontend against a well-documented identity API.
Strengths
- +Clean Apache-2.0 license with no enterprise-only carve-out directory, unlike several peers
- +Headless-by-design means zero UI lock-in — build exactly the login experience your product needs
- +Pairs well with companion Ory projects (Hydra for OAuth2/OIDC server, Keto for permissions) for teams that need the full stack
- +Strong documentation and a security-first design philosophy from the Ory team
Trade-offs
- −Headless-only means you must build and maintain your own login/registration UI — meaningfully more upfront engineering work than Auth0's Universal Login or authentik's flow builder
- −Running the full picture (Kratos + Hydra + Keto) for OAuth2/OIDC server capability adds operational complexity beyond a single service
- −Smaller ecosystem of ready-made UI kits/themes compared to Keycloak or authentik
Free / self-host under Apache-2.0; Ory Network offers a managed hosted version with a free tier and paid usage-based plans for teams that prefer not to operate it themselves. #4
ZITADEL
A cloud-native, API-first identity platform with a generous self-hosted core.
82
OPEN SOURCEAGPL-3.0SELF-HOSTLOCAL-FIRST
ZITADEL is a modern identity and access management platform built API-first for cloud-native and multi-tenant SaaS use cases. It supports OIDC, SAML, passkeys/WebAuthn, and fine-grained actions/hooks for customizing the auth flow in code, and offers both a managed cloud and a self-hostable core.
Strengths
- +Strong native support for passkeys/WebAuthn and modern passwordless flows out of the box
- +API-first design and 'Actions' hooks make custom auth logic (e.g. custom claims, external calls during login) straightforward without forking the codebase
- +Built for multi-tenancy (organizations/projects) from the ground up, closer to Auth0's B2B model than most self-hosted options
- +Active development with frequent releases and a responsive open-source community
Trade-offs
- −AGPL-3.0 requires that any modified version offered as a network service also be released under AGPL — a real legal consideration for SaaS companies embedding it
- −Younger project than Keycloak with a smaller track record at very large scale
- −Some advanced features are positioned toward the paid ZITADEL Cloud tier rather than the self-hosted core
Free / self-host under AGPL-3.0; ZITADEL Cloud offers a managed free tier plus paid usage-based plans for teams that don't want to run the server themselves. #5
SuperTokens
A developer-friendly, self-hostable auth core built for fast integration into existing apps.
80
OPEN SOURCEApache-2.0 (core); ee/ subdirectory carries its own separate license for paid enterprise featuresSELF-HOSTLOCAL-FIRST
SuperTokens is an authentication solution built to drop into an existing app quickly, with official SDKs for popular frontend and backend frameworks and pre-built session-management, MFA, and passwordless flows. It ships a self-hostable core service plus a managed cloud option, aimed at teams that want Auth0-like integration speed without the recurring per-MAU cost.
Strengths
- +Genuinely permissive Apache-2.0 core license for self-hosting the base authentication service
- +SDK-first design with strong framework coverage makes initial integration noticeably faster than headless-only alternatives
- +Built-in session-management primitives (rotating refresh tokens, anti-CSRF) are handled for you rather than left to the integrator
- +Free self-hosted core has no MAU cap, unlike Auth0's metered model
Trade-offs
- −Enterprise SSO/SAML and some advanced MFA policies live behind the separately-licensed ee/ directory, not the free core — verify feature-tier fit before committing
- −Smaller community and third-party plugin ecosystem than Keycloak
- −Fewer built-in identity-brokering options (LDAP, legacy enterprise directories) than Keycloak or authentik out of the box
Free / self-host for the Apache-2.0 core; a managed SuperTokens cloud and a paid Enterprise tier (SSO/SAML, advanced MFA policies under the ee/ license) are available for teams that want those features or don't want to self-host.