Open Source Alternatives to Auth0

TL;DR

Auth0 costs $23+/month for 1,000 monthly active users and gets expensive fast. Three compelling open source alternatives in 2026: Keycloak (Apache 2.0, ~23K stars, Java) is the battle-tested enterprise identity platform — powerful but complex. Zitadel (Apache 2.0, ~8K stars, Go) is the modern cloud-native identity server with excellent developer experience. Logto (MPL 2.0, ~9K stars, TypeScript) is the newest contender — beautiful UI, fast setup, developer-focused. Also note Authentik (covered separately) as another strong option.

Key Takeaways

• Keycloak: Most battle-tested, enormous feature set, complex admin UI, high RAM (~512MB–1GB)
• Zitadel: Modern Go service, excellent API, multi-tenancy, ~100MB RAM
• Logto: Best onboarding experience, TypeScript, modern UI, good for startups and SaaS
• All support: OAuth2, OIDC, SAML 2.0, MFA (TOTP + WebAuthn/Passkeys), social login
• Auth0 pricing trap: $23/month at 1K MAU → $240/month at 7K MAU → $800+/month at 50K MAU
• Self-hosted cost: $5–20/month VPS regardless of user count

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Feature Comparison

Feature	Keycloak	Zitadel	Logto	Auth0
License	Apache 2.0	Apache 2.0	MPL 2.0	Proprietary
GitHub Stars	~23K	~8K	~9K	—
Language	Java	Go	TypeScript	—
OAuth2/OIDC	Yes	Yes	Yes	Yes
SAML 2.0	Yes	Yes	No	Yes
MFA (TOTP)	Yes	Yes	Yes	Yes
Passkeys	Yes	Yes	Yes	Yes
Social login	Yes	Yes	Yes	Yes
LDAP/AD	Yes	Yes	No	Yes
Multi-tenancy	Organizations	Yes (native)	Yes	Yes
Machine-to-machine	Yes	Yes	Yes	Yes
Admin UI	Complex	Good	Excellent	Excellent
RAM (idle)	~512MB–1GB	~100MB	~200MB	—
Price (cloud)	Free	Free (cloud free tier)	Free (cloud free tier)	$23+/mo (1K MAU)

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Option 1: Keycloak — Enterprise Battle-Tested

Keycloak is the most mature and feature-rich option. Used by Red Hat, banks, governments, and enterprises worldwide.

Docker Setup

services:
  keycloak-db:
    image: postgres:16-alpine
    restart: unless-stopped
    environment:
      POSTGRES_DB: keycloak
      POSTGRES_USER: keycloak
      POSTGRES_PASSWORD: "${POSTGRES_PASSWORD}"
    volumes:
      - keycloak_db:/var/lib/postgresql/data

  keycloak:
    image: quay.io/keycloak/keycloak:latest
    container_name: keycloak
    restart: unless-stopped
    ports:
      - "8080:8080"
    command: start
    environment:
      KC_DB: postgres
      KC_DB_URL: jdbc:postgresql://keycloak-db:5432/keycloak
      KC_DB_USERNAME: keycloak
      KC_DB_PASSWORD: "${POSTGRES_PASSWORD}"
      KC_HOSTNAME: "auth.yourdomain.com"
      KC_PROXY: "edge"    # Behind reverse proxy
      KEYCLOAK_ADMIN: admin
      KEYCLOAK_ADMIN_PASSWORD: "${ADMIN_PASSWORD}"
    depends_on:
      - keycloak-db

auth.yourdomain.com {
    reverse_proxy localhost:8080
}

Keycloak Concepts

• Realm: An isolated tenant (create one per environment: dev, prod)
• Client: An application that uses Keycloak for auth
• User: A person who can log in
• Role: Permission assigned to users or groups
• Identity Provider: External login (GitHub, Google, LDAP)

Configure a Client (OIDC)

1. Admin Console → Your Realm → Clients → Create Client
2. Client type: OpenID Connect
3. Client ID: myapp
4. Valid redirect URIs: https://myapp.yourdomain.com/*
5. Copy Client Secret from Credentials tab

In your app:

OIDC_ISSUER=https://auth.yourdomain.com/realms/myrealm
OIDC_CLIENT_ID=myapp
OIDC_CLIENT_SECRET=your-client-secret

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Option 2: Zitadel — Modern Cloud-Native

Zitadel is built in Go, cloud-native from the ground up, with excellent multi-tenancy and a developer-friendly API.

Docker Setup

services:
  zitadel:
    restart: always
    image: ghcr.io/zitadel/zitadel:stable
    command: start-from-init --masterkey "${ZITADEL_MASTERKEY}" --tlsMode disabled
    environment:
      ZITADEL_DATABASE_POSTGRES_HOST: db
      ZITADEL_DATABASE_POSTGRES_PORT: "5432"
      ZITADEL_DATABASE_POSTGRES_DATABASE: zitadel
      ZITADEL_DATABASE_POSTGRES_USER_USERNAME: zitadel
      ZITADEL_DATABASE_POSTGRES_USER_PASSWORD: "${POSTGRES_PASSWORD}"
      ZITADEL_DATABASE_POSTGRES_ADMIN_USERNAME: postgres
      ZITADEL_DATABASE_POSTGRES_ADMIN_PASSWORD: "${POSTGRES_PASSWORD}"
      ZITADEL_EXTERNALDOMAIN: "auth.yourdomain.com"
      ZITADEL_EXTERNALPORT: "443"
      ZITADEL_EXTERNALSECURE: "true"
    ports:
      - "8080:8080"
    depends_on:
      db:
        condition: service_healthy

  db:
    restart: always
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: "${POSTGRES_PASSWORD}"
    volumes:
      - zitadel_db:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s

# Generate masterkey:
openssl rand -base64 32

docker compose up -d

Create an Application in Zitadel

1. Login with initial admin credentials (shown in startup logs)
2. Console → Projects → Create New Project
3. Applications → New Application → Web
4. Authentication Method: PKCE (for frontend) or CODE (for backend)
5. Redirect URIs: https://myapp.yourdomain.com/auth/callback
6. Copy Client ID

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Option 3: Logto — Best Developer Experience

Logto (MPL 2.0, ~9K stars, TypeScript) has the best onboarding and admin UI. Great for SaaS builders.

Docker Setup

services:
  logto:
    image: svhd/logto:latest
    container_name: logto
    ports:
      - "3001:3001"    # Management API + Admin
      - "3000:3000"    # OIDC endpoint
    environment:
      DB_URL: postgresql://logto:${POSTGRES_PASSWORD}@db:5432/logto
      ENDPOINT: "https://auth.yourdomain.com"
      ADMIN_ENDPOINT: "https://logto-admin.yourdomain.com"
    depends_on:
      db:
        condition: service_healthy
    entrypoint: ["sh", "-c", "npm run cli db seed -- --swe && npm start"]

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_DB: logto
      POSTGRES_USER: logto
      POSTGRES_PASSWORD: "${POSTGRES_PASSWORD}"
    volumes:
      - logto_db:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U logto"]
      interval: 10s

auth.yourdomain.com {
    reverse_proxy localhost:3000
}

logto-admin.yourdomain.com {
    reverse_proxy localhost:3001
}

Add Social Login (GitHub example)

1. Admin Console → Connectors → Social → GitHub
2. Enter GitHub OAuth App Client ID + Secret
3. Enable "Sign in with GitHub" button on login page

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Which to Choose

Choose Keycloak if:

• Enterprise with SAML requirements (Salesforce, Azure AD, enterprise SSO)
• LDAP/Active Directory integration needed
• Large team with complex role/permission hierarchies
• You have Java expertise for customization

Choose Zitadel if:

• Multi-tenant SaaS product where each customer is an "organization"
• You want machine-to-machine (M2M) auth with a clean API
• Modern Go stack, low RAM footprint
• Event-driven architecture (Zitadel uses event sourcing internally)

Choose Logto if:

• Developer-focused product with a polished login UI
• You want the fastest time-to-working-auth
• TypeScript ecosystem (Logto SDKs are excellent)
• Building a consumer or B2B SaaS where UX of the login page matters

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See all open source authentication and identity tools at OSSAlt.com/categories/authentication.