Which method is predominantly used in federated identity environments?

In federated identity environments, SAML (Security Assertion Markup Language) is predominantly used because it is designed specifically for exchanging authentication and authorization data between parties, particularly across different security domains. SAML facilitates Single Sign-On (SSO) capabilities, allowing users to authenticate once and gain access to multiple applications without needing to log in again.

The protocol uses XML-based messages to communicate between an identity provider (IdP), which verifies user identity, and a service provider (SP), which provides access to the requested resources. This is particularly advantageous in a federated identity system where organizations want to collaborate and share access while maintaining security standards.

While other options like OpenID, OAuth, and WS (Web Services) have their own use cases in identity and authorization management, they do not specifically target federated identity scenarios with the same level of integration and support for cross-domain security that SAML provides. OpenID is more focused on user-centric authentication over the web, OAuth primarily deals with authorization rather than authentication, and WS is a broader framework that does not explicitly relate to federated identity issues. Hence, SAML stands out as the most appropriate choice in this context.