Authentication is fundamental, but proprietary platforms like Firebase Auth often come with trade-offs, vendor lock-in, opaque internals, and limits on extensibility. For teams who want control, transparency, and flexibility, open source alternatives offer powerful options that are scalable, secure, and developer-friendly. Below are three standout choices that meet real-world needs without compromising developer experience.
SuperTokens
SuperTokens gives you the tools to implement secure login flows with a clear, modular architecture that keeps your front-end fast and your back-end clean. Its SDKs cover modern stacks, from React to Go, and the system is smartly divided: a Frontend SDK for token handling and UI, a Backend SDK for session management and authentication logic, and a Core service that handles low-level tasks. The setup lets you plug in traditional email/password, passwordless, or social login quickly, and then go deeper with advanced features like multi-tenancy, enterprise SSO, and MFA. If you're building for web or mobile, or juggling multiple services, SuperTokens keeps everything coordinated and under your control.
Ory
Ory Kratos is for developers who want an API-first identity layer that doesn’t come with unnecessary baggage. It’s lightweight, just a few megabytes, and designed to run in cloud-native environments, whether that’s Kubernetes or a bare-metal server. Identity workflows like registration, login, passwordless auth, MFA, and account recovery are all built in, backed by open standards like OIDC and SAML. Its headless nature makes it easy to design exactly the user experience you want while maintaining robust backend controls. With Kratos, everything is exposed through stable APIs, and the infrastructure is tuned for scale. It powers billions of secure requests every day and is backed by a vibrant developer community.
Zitadel
ZITADEL blends developer ergonomics with enterprise-grade features. You get modern authentication protocols out of the box, OAuth2, OIDC, SAML, and support for passkeys, MFA, LDAP, and custom tokens. What makes ZITADEL stand out is its deep support for multi-tenancy and customization. Whether you're managing a B2B SaaS platform or nested organizational hierarchies, ZITADEL lets you delegate access control, brand experiences per tenant, and even inject custom logic with event-driven Actions. It’s fully API-driven and built with security at the core: from audit trails to federated logins, JWT profiles to machine accounts. Self-host or go fully managed, you get the same performance and control.