What is the difference between SSO and AD federation?

SSO vs. ADFS: Understanding the Differences in Single Sign-On

Single Sign-On (SSO) has become a cornerstone of modern access management, simplifying user experience and boosting productivity. However, the term often gets conflated with specific implementations, particularly Active Directory Federation Services (ADFS). While both aim to provide seamless access to multiple applications, crucial differences exist in their scope, functionality, and deployment.

At its core, SSO is a broad concept encompassing any technology that allows users to authenticate once and gain access to multiple applications without re-entering credentials. This can involve various protocols and technologies, spanning different operating systems and platforms. Think of it as the overarching goal: a unified, frictionless login experience. Achieving this goal can be done in several ways, including SAML, OpenID Connect, Kerberos, and others. The flexibility of SSO allows integration with a diverse range of applications, from cloud-based SaaS platforms to legacy on-premises systems.

ADFS, on the other hand, is a specific implementation of SSO developed by Microsoft. It's a Windows-centric solution primarily designed to federate identities within a Microsoft environment. ADFS acts as a security token service (STS), verifying user identities against Active Directory and issuing security tokens allowing access to resources within the federated trust. This means its primary strength lies in integrating various Microsoft applications and services, such as Exchange, SharePoint, and Azure applications.

Here's a table summarizing the key distinctions:

Think of it this way: SSO is the concept of a single login for multiple applications; ADFS is a specific tool primarily used within a Microsoft environment to achieve that concept. You can have SSO without ADFS, using a range of alternative solutions, but you can't have ADFS without implicitly having a form of SSO.

Choosing between SSO and a solution like ADFS depends entirely on your organizational needs. If your infrastructure is largely Microsoft-based and you need seamless integration within that ecosystem, ADFS might be a suitable choice. However, for organizations with a diverse application landscape including non-Microsoft applications or cloud-based services, a more comprehensive and flexible SSO solution, employing protocols like SAML or OAuth 2.0, is generally preferred. In some cases, organizations might even utilize both – leveraging ADFS for internal Microsoft applications and a broader SSO solution for external and third-party applications.