Open Source Authentication & Identity Projects
Solutions for managing user authentication, single sign-on, and identity verification across applications.
Keycloak
Open-source identity and access management with SSO, OAuth2, OIDC, and SAML support for modern applications.
Alternative to: 
Auth0
Auth0
Stack Auth
Open-source authentication platform for Next.js and React, built as an alternative to Auth0 and Clerk.
Alternative to: Auth0
Auth0
SuperTokens
Open-source authentication solution, an alternative to Auth0 and Firebase Auth that you can self-host.
Alternative to: Auth0
Auth0
Tinyauth
The tiniest OpenID Certified self-hosted authentication and authorization server, with OAuth, OIDC, LDAP, 2FA, and Traefik/Nginx/Caddy middleware support.
Alternative to: Auth0
Auth0