Auth0

Auth0 (now part of Okta) provides authentication-as-a-service — social login, MFA, SSO, and user management without building auth yourself. But its pricing ($240+/month for 1,000 MAU with advanced features) and per-MAU cost model create significant expenses as your user base grows.

Keycloak is the enterprise standard for self-hosted identity management — SSO, SAML, OIDC, LDAP, and user federation with a battle-tested codebase used by organizations worldwide. Authentik provides a modern alternative with a cleaner UI, proxy-based application protection, and easier setup. Logto focuses on developer experience with beautiful login pages, social login integrations, and a modern architecture built for SaaS products.

The per-MAU pricing model is Auth0's biggest vulnerability. At 10,000 MAU, Auth0's cost reaches $1,500+/month. Self-hosted Keycloak or Authentik handles unlimited users for the cost of a VPS ($20-40/month). For growing SaaS products, the savings compound dramatically — at 100,000 MAU, Auth0's custom pricing reaches thousands per month while self-hosted alternatives remain at fixed infrastructure costs.

The trade-off is operational responsibility. Auth0 handles uptime, security patches, and infrastructure for you. Self-hosted auth means you're responsible for keeping the service running and secure. For teams with DevOps capability, this is manageable. For small teams without server management experience, Auth0's managed service has real value.