If you've been in the B2B SaaS space for any amount of time, you've likely experienced that pivotal moment when an enterprise prospect asks, "Do you support SSO?” and your entire sales cycle hangs in the balance.
But implementing SSO isn't just about checking a box on an enterprise security questionnaire—it's about enabling customers to securely integrate your product into their existing identity infrastructure.
Rather than scrambling to build authentication from scratch when your enterprise clients demand it, SaaS organizations typically go for an open-source SSO solution that could save months of engineering effort.
Before diving into specific solutions, let's establish a solid understanding of how SSO actually works. This foundation will help you evaluate options more effectively.
The core SSO mechanism
SSO allows users to securely access multiple applications and websites using a single set of login credentials. For instance, an enterprise can authenticate their employees to access Slack, Zoom, Notion or your app with their preferred identity provider.
This is what a typical SSO flow looks like:
- User attempts to access an application (Service Provider or SP). In this case your app
- Application redirects to a enterprise's preferred Identity Provider (IdP. For example, Okta)
- User authenticates with the IdP (if not already authenticated)
- On successful authentication by IdP, it creates a session and issues an ID token
- ID token is validated by the application and uses the user profile information to successfully authenticate users and login
- The application also creates a local session and grants access
- When accessing more applications, the global session is recognized, eliminating the need for re-authentication
This flow becomes complex in enterprise environments where multiple protocols, legacy systems, and strict security requirements come into play.
When should you consider open-source SSO authentication?
There are certain scenarios where opting for an open-source authentication system is makes sense.
- Early-stage or MVP products: If your SaaS is in its early days or you’re building a quick MVP, you might not have the budget (or user volume) to justify a paid SSO service. Open-source SSO providers let you add SSO capabilities without breaking the bank.
- Needing more control or customizability: Some teams prefer open-source SSO because it gives them full control over the authentication process and user data. You might have specific custom authentication flows in mind, unique UX requirements, or policies that off-the-shelf services don’t support.
In short, open-source authentication makes a lot of sense for startups and teams who want to save development and licensing costs, retain flexibility, and maintain control. If you have the in-house skills (or willingness to learn) to deploy and manage an identity service, you can implement SSO relatively cheaply and tweak it to your requirements.
Open-source SSO solutions
Now, let's explore the leading open-source SSO solutions and what they’re best for. All of these are free to use (you can self-host them), and they support standard protocols like SAML or OIDC to integrate with enterprise identity systems.
Keycloak: Enterprise-ready all-rounder
Keycloak has become the de facto standard for open-source identity management. Its core strength is its comprehensive feature set and enterprise readiness.
Keycloak uses a “realm-based” architecture where each realm is a logical container for users, applications, and configuration settings. This model makes Keycloak particularly well-suited for multi-tenant deployments.
Key features
- Support for multiple protocols: SAML, OIDC, OAuth 2.0
- Realm-based multi-tenancy for isolating enterprise customers
- Customizable admin console
- Fine-grained authorization capabilities
- Multi-factor authentication
- User federation (LDAP/AD integration)
- Realm-based multi-tenancy
Limitations
- Resource-intensive compared to lighter alternatives
- Steep learning curve for advanced configurations
💡 Real-world usage: Read how payroll and HR solution company Gusto successfully deployed Keycloak for enterprise SSO needs.
Dex: Kubernetes-native identity broker
Dex primarily functions as an identity broker, connecting various enterprise IdPs to your applications through a unified OIDC interface. While it doesn't inherently manage users or sessions, Dex can function as a lightweight IdP if needed.
Key features
- Ultra-lightweight (single binary, small memory footprint)
- Connector system supporting enterprise IdPs (Azure AD, Okta, Google Workspace)
- LDAP and SAML connectors for traditional enterprise
- Designed for Kubernetes environments
- Stateless design for scalability
- Handles identity federation with minimal configuration
Limitations
- Primarily defers authentication to other providers and doesn't inherently manage users or sessions
- Limited built-in user management features
- Lacks a comprehensive graphical user interface (GUI) for configuration
Trivia: Both Keycloak and Dex are projects of the Cloud Native Computing Foundation, a subsidiary of the Linux Foundation.
Authelia: Web-based auth IdP
A lightweight open-source authentication and authorization platform designed to integrate with web proxies. It enhances the authentication of web applications with features like MFA and SSO. Primarily geared towards securing web-based applications.
Key features
- Integrates directly with web proxies (e.g. Traefik) to intercept requests.
- Enforces authentication based on flexible rules (no auth, single-factor, multi-factor).
- Lightweight with a small memory footprint ****.
- Supports various multi-factor authentication (MFA) methods.
- Has a user-friendly web interface for configuration.
Limitations
- User management is manual and home lab-focused
- Dependent on a web proxy for integration
💡 Real world use case: A home lab user or a small team that hosts web services (like a media server, a file sharing application, or a dashboard) behind a reverse proxy like Traefik.
Authentik: Modern, integration-focused IdP
Modern and extensible IdP with a strong emphasis on OAuth 2.0. It offers a wide array of integration options, aiming to be an enterprise-ready solution for authentication and authorisation.
Key features
- Offers numerous plugins for integrating with various identity providers (Active Directory, Google, Microsoft, etc.)
- Provides a web-based interface for connection management
- Supports creating applications and configuring authentication providers
Limitations
- Has an extensive feature set which might make initial setup complex
- Some developers have found the documentation to be lacking for certain use cases
Gluu Server: Security and compliance-focused
Gluu Server has a strong focus on security and compliance. It’s known for its extensive feature set (e.g. support for FIDO2/WebAuthn, advanced user management, etc.). Gluu is often used by organizations that need a reliable on-prem SSO solution with commercial support options.
Key features
- Enterprise IAM suite
- High security for regulated industries
- Full suite of features, including adaptive authentication, audit logs, FIDO2/WebAuthn, etc.
Limitations
- Steep learning curve for auth beginners
- More expensive to scale
💡 Real world use case: A financial institution uses enterprise-grade SSO from Gluu to authenticate over 100,000 authentications per day.
Zitadel
Zitadel is a modern cloud-native IdP solution tailored for SaaS environments, offering strong multi-tenancy and user self-service features. It prioritizes ease of use with automated processes, reducing the overhead of user and identity management.
Key features
- Supports OIDC and OAuth 2.0
- User self-service and automated management
- Multi-tenant architecture designed for cloud-native apps
- Intuitive UI and API-first approach
Limitations
- Requires understanding of cloud-native concepts
- Some advanced features available in enterprise edition only
Ory: Lightweight, API-driven IdP
Ory provides an API-driven minimalist IdP solution ideal for teams seeking simplicity, scalability, and extensive customization through APIs. Its modular approach allows developers to integrate tailored authentication flows seamlessly into applications.
Key features
- Modular and minimalist
- Strong OAuth 2.0 support
- RESTful API design
Limitations
- API-centric, minimal built-in UI
- Advanced customizations may be complex
💡 Real-world use case: OpenAI leverages Ory to support over 400M weekly active users, creating secure, user-friendly CIAM for their applications.
Challenges of open-source SSO implementations
While open-source SSO can save money and provide flexibility, you should be aware of the potential pitfalls and challenges in using these solutions.
Client wants a single truth-source for user management and SSO. need to be able to deliver a prototype with each service integrated with SSO to show for approval within 4 weeks of signing; final system with branding, policy configuration, etc within 60 days after that.
…Spent the last six hours trying to learn from google on options for self hosting identity, set up an experimental keycloak deployment in my lab to mess around with, but ultimately have come out of the venture more confused than I went in.
— Reddit user
Maintenance and security updates
When you adopt an open-source SSO server, you become responsible for keeping it up-to-date and secure.
Unlike a managed service that pushes updates automatically, you’ll need to stay on top of software upgrades, patches, and security advisories. Open-source projects do release fixes, but the speed and frequency can vary based on the community’s activity.
If a critical vulnerability is discovered, you must ensure you upgrade your deployment promptly – otherwise your authentication system could be at risk.
Here’s what a Reddit user had to say (Slightly paraphrased) about patching.
Keycloak is pretty cool, but if you don’t constantly keep an eye on the vulnerabilities and patch them constantly, you will end up in a bad situation.
Scalability
Not all open-source solutions are plug-and-play for large scale or high availability.
If you anticipate a big user load or need global uptime, you’ll have to architect your open-source SSO provider for scalability. For example, Keycloak can scale, but it may require a different setup with more resources.
Similarly, ensuring high availability (so that SSO isn’t a single point of failure) might mean running multiple instances in failover, which adds complexity.
Integration complexity
Getting an open-source SSO solution to work with all your customers’ identity setups can be complex. Enterprise IdP integrations (setting up SAML trust, mapping attributes, handling metadata) can be tricky to configure and debug, especially if you’re not already familiar with the protocols.
Open-source systems offer flexibility, but that often means a lot of knobs to turn. You might have to sift through documentation and community forums to figure out how to, say, get SAML working with a particular Azure AD configuration. This can be a time sink for your engineers and developers.
Here’s a perspective from Reddit:
I personally wanted to do SSO myself, but I eventually gave up on it; too many services didn't support SSO which caused more problems for me. It ended up requiring many services to be wrapped in another layer of authentication, now requiring the user to login twice (once for SSO and another for the service's own authentication). Unfortunately, this also breaks any mobile applications for said services, which isn't worth the benefits of SSO.
Documentation and support gaps
Open-source projects vary in documentation quality. Some have excellent docs and active communities; others might have sparse or outdated documentation that leaves you guessing.
You may run into issues where the only solution is buried in a GitHub issue or a community Slack channel. The lack of official support can be a challenge when you hit a roadblock – you can’t pick up the phone and call the vendor.
Accelerating enterprise deals with third-party SSO solutions
Implementing SSO can quickly become mission-critical, especially when lucrative enterprise deals are on the line. Enterprise clients frequently list SSO integration as a non-negotiable requirement. While open-source solutions offer substantial flexibility, they often come with integration complexities, maintenance overhead, and longer timelines—potentially delaying critical sales.
In scenarios like these, turning to specialized third-party authentication providers can offer significant advantages. Solutions like Scalekit simplify SSO integration, enabling SaaS companies to deploy enterprise-grade authentication flows in a matter of hours rather than weeks or months.
Opting for a third-party solution can be strategic when:
- You have time-sensitive enterprise contracts pending, and lengthy integration processes might risk losing deals
- Your internal engineering resources are limited or better focused on your core product
- Immediate compliance with enterprise security standards and client expectations is mandatory
Leveraging solutions like Scalekit not only accelerates your SSO implementation timeline but also ensures your SaaS is ready to accommodate enterprise authentication requirements, opening doors to faster, smoother enterprise adoption.
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