Logto

Logto is an auth platform you can self-host for free or use their cloud: login, signup, SSO, MFA, and user management for SaaS apps. Drop in their SDK, get a polished login experience, manage users through their admin console, done.

It handles the stuff that's hard to build correctly: OAuth 2.0/OIDC compliance, social login (Google, GitHub, Apple), passwordless auth, MFA, organization management for B2B SaaS, and RBAC (role-based access control, controlling who can do what in your app).

MPL-2.0 license. The self-hosted version is fully featured, no artificial feature gates to push you to cloud.

The catch: auth is a 'get it wrong and you're on the news' category. Logto is well-built but younger than Auth0 or Keycloak. If you self-host, you're responsible for security patches and uptime of your auth system, and that's not something you want going down at 2am.