Best Open Source Backend as a Service Authentication Solutions in 2025

Before diving into the specific solutions, it’s worth noting that implementing robust authentication for applications can be complex and time-consuming. Backend as a Service (BaaS) authentication solutions aim to simplify this process by providing ready-made, secure authentication systems that developers can integrate with minimal effort. This report examines the leading open source options available today.

Understanding BaaS Authentication Requirements

Authentication in modern applications requires multiple features beyond simple username/password verification. Today’s solutions must support:

• Multiple authentication methods (social logins, passwordless options)

• Multi-factor authentication (MFA)

• Role-based access control

• Enterprise-grade security standards

• Integration with existing identity providers

• Support for standard protocols (OAuth 2.0, OpenID Connect, SAML)

The following open source solutions excel in meeting these requirements while offering the flexibility and control of self-hosting.

Top Open Source Authentication Solutions

Keycloak

Keycloak has established itself as one of the most robust and battle-tested open source authentication solutions available.

Key Features

• Identity brokering with multiple social and enterprise identity providers

• Multi-factor authentication and passwordless options

• Comprehensive support for OpenID Connect, OAuth 2.0, and SAML 2.0

• Role-based access control

• Support for organizations and multi-tenancy

Keycloak is particularly well-regarded for production environments, with many developers confirming its reliability: “You can go with ‘keycloak’. It’s open source, battle tested and we, like many others, use it in production at work”1. While its initial configuration can be complex, users report that “it’s definitely worth it in the end”1.

Zitadel

Zitadel positions itself as a modern Keycloak alternative with enhanced developer experience and strong B2B capabilities.

Key Features

• API-first design for developer-friendly integration

• Comprehensive support for multi-tenancy

• Built-in audit trail capabilities

• Multi-factor and passwordless authentication

• Support for OpenID Connect, OAuth 2.0, and SAML 2.0

Zitadel offers three deployment options: “Self-hosting Zitadel open source, Zitadel cloud (which has a free tier), Self-hosting Zitadel with a commercial license”1. It’s particularly suited for applications requiring strong B2B functionality, as it “excels in multi-tenant environments, making it ideal for organizations managing multiple client organizations or separate business units”6.

Appwrite

Appwrite provides a comprehensive BaaS platform with strong authentication capabilities as part of its offering.

Key Features

• Over 30 login methods including Email/Password, SMS, OAuth, Magic URLs

• Support for teams, roles, and user labels

• Rate-limiting and advanced user protection

• Custom SMTP and email templates

• Integration with broader BaaS features like database and storage

Appwrite is described as “an open-source BaaS that provides databases, authentication, file storage, real-time updates, serverless functions, and API management”10. Its Docker-based deployment makes it relatively easy to self-host, and it offers comprehensive SDKs for multiple platforms.

Supabase

Supabase positions itself as an open source Firebase alternative with robust authentication features tied to its database capabilities.

Key Features

• Authentication integrated with Row Level Security (RLS)

• Social login providers

• JWT-based authentication

• Role-based access control

• Native integration with Postgres database

Supabase provides “authentication with RLS”8, making it particularly powerful for applications that need tight integration between authentication and database access control. Its approach simplifies securing database access based on user identity.

Authelia and Authentik

Both solutions offer comprehensive authentication capabilities with support for multiple MFA methods.

Key Features

• Multiple MFA methods: TOTP, WebAuthn, SMS, and more

• Support for various authentication protocols

• Granular role-based access control

• Customization options

These solutions have strong community support, with Authelia having “22.5k GitHub stars and 200+ contributors”14 and Authentik having “14.5k GitHub stars and 330+ contributors”14.

Feature Comparison

When comparing these solutions across key authentication capabilities:

Protocol Support

All major solutions support industry-standard protocols like OAuth 2.0 and OpenID Connect, with most also supporting SAML 2.0 for enterprise integration.

Multi-Factor Authentication

All reviewed solutions provide robust MFA options, with Keycloak, Zitadel, Authelia, and Authentik offering the most comprehensive support for various authentication methods including “TOTP (time-based one-time password), WebAuthn, SMS, OIDC (OpenID Connect), Email, Push, Hardware tokens”14.

Multi-Tenancy

Zitadel stands out for its native multi-tenancy design, making it “ideal for B2B customer and partner management”14. Keycloak has added improved multi-tenancy through its Organizations feature, while other solutions have varying degrees of multi-tenant support.

Self-Hosting Options

All solutions offer self-hosting capabilities, with varying degrees of deployment complexity:

• Appwrite: Docker-based deployment

• Zitadel: “Several deployment options, including Linux, MacOS, Docker compose, Knative, and Kubernetes”14

• Keycloak: Kubernetes via Helm and other options

• Supabase: Docker-based self-hosting

Choosing the Right Solution

The best authentication solution depends on your specific requirements:

For Enterprise B2B Applications

Zitadel and Keycloak are particularly strong choices, with Zitadel offering superior multi-tenancy and Keycloak providing mature enterprise features.

For Comprehensive BaaS Needs

If you need authentication as part of a broader BaaS solution, Appwrite and Supabase offer more integrated approaches with databases, storage, and other backend features.

For Developer Experience

Zitadel emphasizes developer-friendly APIs and integration. As noted in the search results, it’s “engineered for developers, offering a robust array of identity tools that offload complex tasks through solid API abstractions”9.

For Smaller Projects

PocketBase, which is “Go based, with Svelte frontend”16 and uses SQLite, might be more appropriate for smaller projects with simpler authentication needs.

Conclusion

Open source backend authentication solutions have matured significantly, offering enterprise-grade security and features while providing the flexibility of self-hosting. Keycloak and Zitadel stand out for comprehensive identity management, while Appwrite and Supabase excel as part of broader BaaS platforms.

When selecting a solution, consider not only current authentication requirements but also future needs in terms of scaling, multi-tenancy, and integration with other systems. Each solution has its strengths, and the right choice depends on your specific application architecture, development preferences, and business requirements.

As authentication standards and security best practices continue to evolve, these open source solutions demonstrate the industry’s commitment to providing secure, flexible, and developer-friendly authentication options for modern applications.

Citations:

1. https://www.reddit.com/r/Python/comments/1ci9ijz/suggestions_for_a_selfhosted_authentication_as_a/
2. https://blog.elest.io/best-free-open-source-backend-as-a-service-solutions/
3. https://zitadel.com/blog/migrate-from-keycloak
4. https://www.permit.io/blog/top-12-open-source-auth-tools
5. https://vocal.media/01/top-4-open-source-baa-s-platforms
6. https://zitadel.com/blog/zitadel-vs-keycloak
7. https://appwrite.io
8. https://supabase.com
9. https://opensourcealternative.to/alternativesto/auth0
10. https://www.freecodecamp.org/news/backend-as-a-service-beginners-guide/
11. https://github.com/AppFlowy-IO/AppFlowy-Cloud/issues/189
12. https://www.reddit.com/r/opensource/comments/196aggk/comparing_the_best_free_opensource_backend_as_a/
13. https://dev.to/ethanleetech/top-7-backend-as-a-service-baas-for-nextjs-32mc
14. https://research.aimultiple.com/open-source-mfa/
15. https://blog.back4app.com/backend-as-a-service-open-source/
16. https://gist.github.com/PARC6502/ee4db400a05e6eb6d0981bb8cd4e4c1c
17. https://pocketbase.io
18. https://www.reddit.com/r/selfhosted/comments/13rr6i7/keycloak_vs_authentik_vs_authelia_help_choose_sso/
19. https://news.ycombinator.com/item?id=39335096
20. https://news.ycombinator.com/item?id=36388650
21. https://gist.github.com/bmaupin/6878fae9abcb63ef43f8ac9b9de8fafd?permalink_comment_id=4919216
22. https://docs.netbird.io/selfhosted/identity-providers