Authenticate Users with WS-Federation in Web Applications

WS-Federation remains a critical, albeit legacy, authentication protocol in 2026, particularly for bridging modern cloud identity systems with on-premise infrastructures that still operate within a small segment of the enterprise market. Despite the dominance of more contemporary protocols like OIDC and OAuth2, WS-Federation continues to be supported, exemplified by its incorporation into .NET 10, due to its ability to handle "dumb" clients through its Passive Requestor Profile and facilitate hybrid identity architecture. This XML-based protocol, often implemented in environments where newer JSON token systems are incompatible, utilizes a browser-dependent flow involving HTTP redirects and SAML assertions to enable single sign-on (SSO) across disparate systems. While maintaining WS-Federation for existing systems is viable, transitioning to modern authentication methods can be achieved through strategies like the "Strangler Fig" pattern or identity proxies, allowing organizations to modernize securely without extensive code rewrites.