Best Open Source Authentication Solutions in 2026

TL;DR

Auth0 charges $23+ per 1,000 MAU. At 10,000 users, you're paying $2,760/year for a service you could run on a $16/month VPS. Keycloak is the enterprise-grade standard for SSO, SAML, and LDAP federation. Authentik protects existing apps via reverse proxy without touching their code. Logto has the best developer experience for modern web apps. SuperTokens is the easiest drop-in for React/Node.js stacks.

Key Takeaways

Keycloak (Apache-2.0, 23K+ stars) is the most widely deployed open source IAM platform, trusted by Red Hat, governments, and enterprises globally
Authentik (MIT, 13K+ stars) can protect any existing app via reverse proxy without code changes — the fastest path to SSO for legacy services
Logto (MPL-2.0, 9K+ stars) has 15+ SDKs and the cleanest sign-in UI builder for modern consumer-facing apps
SuperTokens (Apache-2.0, 13K+ stars) provides pre-built React UI components and handles sessions securely by default
Ory (Apache-2.0, 14K+ stars) is the cloud-native choice for microservice architectures that need identity as stateless services
Self-hosting auth at 10K MAU saves $2,568/year vs Auth0; at 100K MAU the savings reach $27,216/year

The Hidden Cost of Identity-as-a-Service

Auth0 and Okta price on Monthly Active Users because that's what scales with your business. When you're at 100 MAU, the pricing seems negligible. When you hit 10,000 MAU or 100,000 MAU, the costs become a significant line item — and unlike infrastructure costs, they don't flatten as you scale.

The architectural lock-in is equally significant. Auth0's token format, user metadata schema, and action/rule system are proprietary. Teams that have deeply integrated Auth0 hooks into their authorization logic find migration to an alternative requires weeks of engineering work. Open source alternatives — especially those supporting OIDC and SAML standards — provide a clean exit path whenever you need it.

Keycloak — Enterprise SSO Standard

Keycloak is the reference implementation for enterprise identity management. It's been production-hardened over 10+ years, deployed by Red Hat (its creator), the European Union's identity infrastructure, NASA, and thousands of enterprises globally. If you need SAML federation, LDAP user sync, Kerberos integration, or fine-grained authorization policies, Keycloak is the tool.

The feature set is comprehensive: OIDC, OAuth 2.0, SAML 2.0, LDAP/AD sync, Kerberos, social login, custom authentication flows, user federation, admin REST API, and a custom theme system for white-labeling the login UI.

Authentication flows are Keycloak's most powerful feature. You can build multi-step authentication sequences: email/password → TOTP → IP address check → risk scoring → step-up authentication for sensitive operations. Each step is a "Authenticator" that can be mixed and matched in the admin console.

# Keycloak Docker Compose (with PostgreSQL)
services:
  keycloak:
    image: quay.io/keycloak/keycloak:latest
    command: start-dev  # Use 'start' for production
    environment:
      - KC_DB=postgres
      - KC_DB_URL=jdbc:postgresql://db:5432/keycloak
      - KC_DB_USERNAME=keycloak
      - KC_DB_PASSWORD=password
      - KEYCLOAK_ADMIN=admin
      - KEYCLOAK_ADMIN_PASSWORD=change-me-in-production
      - KC_HOSTNAME=auth.yourdomain.com
    ports:
      - "8080:8080"
    depends_on:
      - db
  db:
    image: postgres:15
    environment:
      POSTGRES_DB: keycloak
      POSTGRES_USER: keycloak
      POSTGRES_PASSWORD: password
    volumes:
      - keycloak_data:/var/lib/postgresql/data
volumes:
  keycloak_data:

Keycloak's Java foundation has a cost: a production Keycloak instance with clustering needs 2–4 GB RAM per node. For small organizations with budget constraints, this is where Authentik or Logto are more appropriate.

Key features:

OIDC, OAuth 2.0, SAML 2.0 support
LDAP and Active Directory sync
Kerberos integration
Custom authentication flows
User federation (import from external sources)
Fine-grained authorization (policy-based)
Social login (Google, GitHub, Microsoft, 50+ providers)
Admin REST API
Custom themes for login pages
Multi-realm (multi-tenant) support

Authentik — Best for Protecting Existing Apps

Authentik's defining capability is its outpost/proxy provider architecture. You deploy an Authentik outpost alongside your applications, and it acts as a forward-auth middleware. When a user tries to access your internal tool, they're redirected to Authentik for authentication, then forwarded back. Your existing application code doesn't change.

This makes Authentik the fastest path to adding SSO to:

Internal tools that have no auth (Grafana without LDAP, internal wikis, admin dashboards)
Applications that support basic auth but not OIDC
Legacy services that you can't easily modify

# Authentik with Nginx forward auth
services:
  authentik-server:
    image: ghcr.io/goauthentik/server:latest
    command: server
    environment:
      - AUTHENTIK_REDIS__HOST=redis
      - AUTHENTIK_POSTGRESQL__HOST=postgresql
      - AUTHENTIK_POSTGRESQL__PASSWORD=password
      - AUTHENTIK_SECRET_KEY=your-secret-key
      - AUTHENTIK_ERROR_REPORTING__ENABLED=false
  authentik-worker:
    image: ghcr.io/goauthentik/server:latest
    command: worker
    environment:
      - AUTHENTIK_REDIS__HOST=redis
      - AUTHENTIK_POSTGRESQL__HOST=postgresql
      - AUTHENTIK_POSTGRESQL__PASSWORD=password
      - AUTHENTIK_SECRET_KEY=your-secret-key

Authentik also supports SCIM provisioning — automatically creating and deactivating user accounts in connected applications when employees join or leave. This is the feature IT teams care about most for employee lifecycle management.

Visual flow builder lets non-developers design authentication sequences through a drag-and-drop interface. Add MFA steps, conditional logic based on user groups, and custom branding without writing code.

Key features:

Forward authentication proxy (protect apps without code changes)
OIDC, SAML, LDAP provider support
SCIM provisioning
Visual flow builder for authentication sequences
Application proxy (outpost)
Passkeys/WebAuthn support
Radius provider (for network authentication)
Custom branding per application

Logto — Best Developer Experience

Logto is built specifically for developers building modern web and mobile applications. The focus shows: the documentation is excellent, the SDK selection covers 15+ frameworks, and the hosted sign-in experience is polished out of the box.

The sign-in UI is customizable through a UI editor without CSS skills required. You choose your logo, colors, and layout — Logto renders a pixel-perfect sign-in page. This is the feature Auth0 charges significantly for in their higher tiers.

Multi-tenancy is a first-class feature in Logto. If you're building a B2B SaaS where each customer is a separate "organization," Logto's organization concept maps directly to that model. Each organization can have its own SSO configuration, branding, and member management.

// Logto Next.js SDK
import LogtoClient from '@logto/next'

export const logtoClient = new LogtoClient({
  appId: 'your-app-id',
  appSecret: 'your-app-secret',
  endpoint: 'https://auth.yourdomain.com',
  baseUrl: 'https://yourapp.com',
  cookieSecret: 'complex-secret-at-least-32-chars',
  cookieSecure: process.env.NODE_ENV === 'production',
})

Key features:

15+ official SDKs (Next.js, React, Vue, Express, Go, Python, etc.)
Visual sign-in UI editor
Multi-tenancy with organization concept
Social login (30+ providers)
Webhooks for user events
Audit logs
TypeScript-native API

SuperTokens — Easiest Drop-In Auth

SuperTokens differentiates by providing pre-built UI components for the most common authentication flows: email/password, social login, magic links, and passwordless. If your frontend is React, you import the SuperTokens React component library and get a complete auth UI in an afternoon.

The session management is particularly well designed. SuperTokens rotates refresh tokens on every use, short-lived access tokens (1 hour), and handles token theft detection with automatic session revocation. These security properties are correct by default without requiring developer configuration.

SuperTokens self-hosted is Apache-2.0 licensed and runs as a service alongside your backend. Your backend uses the SuperTokens SDK to verify tokens, which calls the SuperTokens core service.

Ory — Cloud-Native Microservices

Ory takes an architecture-first approach: each concern (identity, sessions, permissions, OAuth) is a separate service. Ory Kratos handles identity, Ory Hydra handles OAuth 2.0, Ory Keto handles permissions. This modularity suits microservice architectures where you want identity to be a stateless service rather than a monolith.

The trade-off is operational complexity: you're running and maintaining multiple services. Ory is worth the complexity for large teams with dedicated platform engineers, but is over-engineered for most applications.

Full Comparison

Feature	Keycloak	Authentik	Logto	SuperTokens	Ory
Protocol Support	OIDC, SAML, LDAP	OIDC, SAML, Proxy	OIDC	OIDC	OIDC, OAuth
Min RAM	2 GB	1 GB	512 MB	512 MB	512 MB
Language	Java	Python/Go	TypeScript	Java/Node	Go
SAML 2.0	✅	✅	Roadmap	❌	❌
LDAP Sync	✅	✅	❌	❌	❌
Proxy Auth	❌	✅ Native	❌	❌	❌
Multi-Tenant	✅ (realms)	✅	✅ (orgs)	✅	✅
Pre-built UI	✅ Themes	✅	✅ Custom	✅ Components	❌
Social Login	✅ 50+	✅	✅ 30+	✅	✅
License	Apache-2.0	MIT	MPL-2.0	Apache-2.0	Apache-2.0

Decision Framework

Choose Keycloak if: Enterprise requirements — SAML federation, LDAP sync, fine-grained authorization, or compliance requirements demand a battle-tested IAM platform.

Choose Authentik if: You need to add SSO to existing apps without modifying their code. Also the best choice for protecting internal tools and self-hosted services.

Choose Logto if: You're building a consumer or B2B SaaS and want the best SDK coverage and sign-in UI experience.

Choose SuperTokens if: Your stack is React + Node.js/Python and you want pre-built UI components with correct session security defaults.

Choose Ory if: You're building a microservice architecture and want identity as composable, stateless services.

Cost Comparison

MAU	Auth0 Annual	Keycloak (self-hosted)	Annual Savings
1K	$276	$96/year (VPS)	$180
10K	$2,760	$192/year	$2,568
100K	$27,600	$384/year	$27,216

Auth0's cost scales linearly with users. Self-hosted auth cost scales with infrastructure, which grows much more slowly.

See open source alternatives to Auth0 on OSSAlt.

Best Open Source Auth Solutions in 2026

Best Open Source Authentication Solutions in 2026

TL;DR

Key Takeaways

The Hidden Cost of Identity-as-a-Service

Keycloak — Enterprise SSO Standard

Authentik — Best for Protecting Existing Apps

Logto — Best Developer Experience

SuperTokens — Easiest Drop-In Auth

Ory — Cloud-Native Microservices

Full Comparison

Decision Framework

Cost Comparison

The SaaS-to-Self-Hosted Migration Guide (Free PDF)