Top 5 Open Source SSO Solutions (Pros, Cons And What to Watch Out For)

These days, SSO is a must-have - nobody wants to remember yet another password for your app. The good news is, thanks to open source SSO solutions, SaaS developers like yourself can add SSO to their apps without breaking the bank.

But with so many options out there, how do you zero in on the right one for your app?

In this article, we'll walk you through what to watch out for when choosing an open source SSO solution, then we’ll give you a rundown of five providers worth considering and finally talk about why sometimes, a hosted SSO provider is the better option.

What is an open source SSO provider?

A Single Sign-On (SSO) provider is software designed to centralize user authentication, by letting users log in once and access multiple apps without repeated logins.

Open source SSO providers share their source code publicly and encourage collaboration within the development community. They’re usually free to use, but some may offer more advanced features in their paid versions. It's also worth noting that they may have fewer features compared to their commercial counterparts – the specific features will depend on the individual provider. Always check the docs, licensing terms, and the distinctions between the free and paid versions (if any) of the provider you want to support in your SaaS.

What to look for in an open source SSO solution

When choosing an open source Single Sign-On (SSO) solution, keep these key factors in mind:

• Protocol support: Chances are, your customer's identity providers use different SSO protocols. Opt for a provider that supports the most widely used standards, including SAML and OpenID Connect for broad compatibility.
• Security features: Prioritize providers offering additional authentication options, such as Multi-Factor Authentication (MFA) for extra security.
• Specific IdP Support: Ensure that the SSO provider supports the identity providers you plan to connect your SaaS to. Common IdPs include Active Directory, social identity providers (e.g., Google, Facebook), and other authentication sources. Check if it has pre-integrations and straightforward configuration options. The setup process should be clear with easy-to-follow documentation.
• User-friendly login flows: Ensure the SSO solution offers a seamless login experience across all platforms—web, mobile, and desktop. You may also want the option to customize the UI to match your branding.
• Regular updates: Look for a solution backed by a vibrant community or even better, dedicated developer support that regularly updates the software to address security vulnerabilities. Check forums, mailing lists, and GitHub repositories for activity levels.
• High availability: Choose an SSO solution designed for high availability, capable of scaling graciously with your user base.
• Seamless integration: The solution should integrate smoothly with your existing infrastructure. Look out for accessible APIs or SDKs accompanied by thorough, user-friendly documentation to simplify the setup and troubleshooting process.
• Cost-effectiveness: Even though the solution is open source, consider the total cost of ownership, including deployment, customization, and maintenance expenses.

The top 5 open source SSO providers

• ‍Keycloak for end-to-end identity management beyond SSO.
• Central Authentication Service for enterprise-grade SSO for web apps.
• FreeIPA for SSO in Linux systems.
• Authelia for a fast and lightweight SSO solution.
• IdentityServer for headless SSO in .NET apps.

Below are 5 open source SSO solutions you should consider:

Keycloak

Keycloak is an open source identity management solution developed by Red Hat. Beyond SSO, it enables user federation, identity brokering (connecting with external identity providers), and fine-grained authorization. You can integrate keycloak into your app using the APIs and client libraries (for languages such as Java and JavaScript) it provides.

Pros of Keycloak

• Comprehensive protocol support: Keycloak supports two of the most popular SSO protocols – OpenID Connect (OIDC) and SAML 2.0 making it highly versatile and compatible with a wide range of apps including web and mobile.
• Third-party integrations: Keycloak comes with a lot of third-party integrations (like Google, FB, Twitter, StackOverflow, etc) out-the-box.
• External identity source sync: In case your customer uses some type of user directory, Keycloak allows you to synchronize with those directories - whether they're standard ones like Active Directory (which it supports by default), or custom databases (which you can support using the Keycloak User storage API).
• Customization: Keycloak lets you customize all user-facing login pages. With support for the FreeMarker Template Language (or .ftl files), you can use HTML, CSS styles, or JS scripts to tweak the UI until it matches your brand identity.

Cons of Keycloak

• Steep learning curve: The extensive functionality and configuration options can be overwhelming if you don’t know a lot about configuring IAM systems. You’ll need to invest considerable amounts of hours to comb through the docs and test your integration.
• Scalability issues: Scalability may require additional setup and optimization like setting up multi-site deployments and having processes in place to sync data between sites if they go out of sync. Luckily, there’s a whole section in the docs dedicated to ensuring high availability.
• Documentation and examples: Although Keycloak's documentation is thorough, it’s difficult to navigate especially if you’re searching for particular information. It also lacks practical and end-to-end examples you’d see in other SSO providers.

There are several Keycloak distributions to choose from:

• Server: A standalone application downloadable as a tar or zip file.
• Container image: Distribution appropriate for Docker, Podman, Kubernetes, and OpenShift.
• Operator: Distribution for Kubernetes and OpenShift based on Operator SDK.

All three can be downloaded from the Keycloak downloads page.

Central Authentication Service (CAS)

The Central Authentication Service (CAS) is an open source, enterprise-grade single sign-on solution for web apps. It was originally created by Yale University and has since evolved into a widely adopted service managed by the Apereo Foundation. Note, the name CAS also refers to the CAS SSO protocol, which this provider also supports.

Pros of CAS

• Integration capabilities: CAS offers a wide range of integration libraries for various languages and frameworks including Java, .Net, PHP, Perl, Apache, uPortal, and others.
• Support for multiple authentication protocols: CAS supports various authentication protocols, including SAML, OpenID Connect, CAS, and WS-Fed. You can even use it to delegate authentication to social IdPs like Facebook or Twitter.
• Admin UIs: It provides an admin console that you can use to administer and manage the CAS server deployment.
• Customizable login pages: CAS allows you to edit the CSS and HTML files or even add JavaScript effects to match your branding and UI guidelines. You can also localize messages to suit your customer’s language needs.

Cons of CAS

• Complexity in setup and configuration: Deploying and configuring CAS can be complex, especially if you don’t have a dedicated engineering team with expertise in identity management.
• Learning curve: It has a very steep learning curve – you’ll need to study its architecture and the multiple configuration options.
• Operational overhead: Maintaining a CAS server, especially in a high-availability environment, can introduce operational overhead in terms of monitoring, scaling, and updating it. Fortunately, like KeyCloak, it has a high-availability guide you can refer to.

Where to get CAS

CAS recommends building and deploying locally using the WAR Overlay method which you can find in the docs.

FreeIPA

FreeIPA (Identity, Policy, Audit) is an integrated security information management solution that combines identity management (directory services), policy (configuration management), and audit into a single, cohesive framework. It’s a bit different from the providers on this list since it focuses on managing identities specifically for Linux users.

Pros of FreeIPA

• It’s an all-in-one authentication service: Besides SSO, it allows admins to define and enforce policies for access control. It also has a built-in Certificate Authority(CA) that can be used to implement certificate-based authentication.
• Multiple management interfaces: It provides a user-friendly GUI and command-line interface, a JSON-RPC API, and a Python SDK for managing identities and policies – you get to choose which one works best for you.
• Support for standard protocols: It supports SSO protocols like OpenID and Kerberos.

Cons of FreeIPA

• Complexity in setup and maintenance: Even though it’s not as complicated as CAS, the initial setup and ongoing maintenance of FreeIPA can be complex, particularly in large or distributed environments.
• Focused on Linux/UNIX: While it offers significant advantages for Linux/UNIX systems if your environment doesn’t use Linux or has a mix of other OSs, you’ll find it limiting.

Where to get FreeIPA

Download and start using the latest FreeIPA release from the downloads page.

Authelia

Authelia describes itself as the Single Sign-On Multi-Factor portal for web apps. It enables SSO via session cookies, OpenID Connect, or trusted headers.

Placed side by side with the providers we’ve discussed so far, Authelia is very lightweight, mostly because it doesn’t offer as many features as the rest do. Beyond SSO, it also enables granular policy definitions, MFA, and identity validation via email.

Pros of Authelia

• Flexible authentication sources: Authelia can integrate with your customer’s existing LDAP directories or Active Directory.
• Intuitive UI: It has a simple login portal whose workflow is completely transparent to your users.
• Fast authentication process: It was created in React and Go and according to Authelia, the login portal has a loading time of 100 milliseconds.

Cons of Authelia

• Limited protocol support: The only identity provider implementation it currently supports is OpenID Connect 1.0 (even then it doesn’t support the OpenID Connect 1.0 relying party role), unlike other SSO solutions that directly support protocols like SAML (a protocol widely used by enterprises).
• Focus on web apps: Authelia is specifically designed for web apps, potentially limiting its applicability to desktop or mobile applications without additional configuration.

Where to get Authelia

See the configuration and deployment documentation to get started with Authelia.

IdentityServer

IdentityServer is an open source Identity and Access Management framework for .NET and offers headless SSO through a developer-friendly API.

It primarily focuses on token-based SSO through the OpenID Connect protocol.

Pros of IdentityServer

• Standards compliant: IdentityServer is fully compliant with OpenID Connect and OAuth 2.0 standards.
• More than just an SSO provider: Identity Server also supports access control for APIs and identity federation.
• Flexible and extensible: It has a modular architecture which makes it easy to extend and integrate with your existing system.

Cons of IdentityServer

• .NET Ecosystem: Being tightly coupled with .NET, IdentityServer might be less appealing if you use other technology stacks.
• Complex to setup and configure: Unlike an alternative like Keycloak, IdentityServer is not a ready-to-run product, you have to set it up and configure it which can get complicated if you don’t usually configure IAM services.
• Pricing: While IdentityServer is open source, it has two versions – the free one and the commercial one. If you want security fixes and regular updates, you’ll have to make annual payments for the commercial version.

Where to get IdentityServer

Visit the IdentityServer homepage to get started.

Consider a hosted SSO provider instead

While open source solutions have their benefits like cost savings and tons of flexibility, they also come with their own set of limitations.

• Limited functionality: Depending on the project, open source SSO solutions might lack certain features found in commercial products or may have slower release cycles for new features and updates.
• Security concerns: Security audits and updates depend heavily on the community's activeness and resources.
• Integration efforts: You need a high level of knowledge of identity management to set up, configure, and manage them.
• Documentation: While some open source projects have excellent documentation others may suffer from outdated, sparse, or overly technical documentation.
• Professional support: Commercial solutions often come with guaranteed support as part of a subscription or license fee, open source projects typically do not offer this level of direct, professional support. You’ll have to turn to Stack Overflow, forums, or GitHub discussions.

Hosted SSO providers solve all of these challenges, allowing you to provide enterprise-grade uptime and reliability to your clients all the while reducing your engineering man-hours spent.

Here’s what you can expect from a hosted SSO provider:

• Simple to manage: You don’t have to install or deploy an SSO solution yourself. And in most cases, the provider will have a web-based UI, SDK, or API that makes the integration process more straightforward.
• Professional Support and Reliability: Most hosted SSO providers include professional support either through calls, Slack, email, etc to help you with any configuration issues or questions you might have.
• Continuous Updates and Feature Releases: Hosted SSO providers are committed to maintaining high standards of service, routinely rolling out new features, and critical security patches without requiring customer intervention.
• Integration ease: Hosted SSO solutions often come with pre-built integrations for popular identity providers and HRIS platforms which further reduces the time and effort needed to build an SSO integration.

Like with the open source SSO solutions we’ve explored above, not every hosted SSO provider will be right for you. However, if you’re building an enterprise app and are looking for a reliable SSO solution, you’ll love WorkOS:

• Get started fast: With SDKs in every popular language, easy-to-follow documentation, and Slack-based support, you can implement SSO in minutes rather than weeks.
• Support every protocol: With OAuth 2.0 integrations to popular providers like Google and Microsoft, compatibility with every major IdP, and full support for custom SAML/OIDC connections, WorkOS can support any enterprise customer out of the box.
• Avoid the back-and-forth: WorkOS’ Admin Portal takes the pain out of onboarding your customers’ IT teams and configuring your app to work with their identity provider.
• Pricing that makes sense: Unlike competitors who price by monthly active users, WorkOS charges a flat rate for each company you onboard - whether they bring 10 or 10,000 SSO users to your app.

Explore Unified SSO by WorkOS.