What is the primary purpose of WS-Federation?

The primary purpose of WS-Federation is to provide a flexible Federated Identity architecture. This standard allows for the interoperability of identity providers and service providers, enabling users to authenticate and gain access across different security domains using a single set of credentials. WS-Federation facilitates the sharing of authentication tokens among multiple applications and services, which enhances user experience by providing Single Sign-On (SSO) capabilities.

This architecture supports scenarios where users belong to multiple organizations or need to access various services without requiring separate logins for each one, thus simplifying identity management and improving security by reducing the number of passwords users must remember.

The other choices do not accurately reflect the primary function of WS-Federation. Storing user credentials securely pertains more to password management and encryption, while managing end-user accounts relates to user administration tasks rather than the federated identity aspect. Additionally, connecting directly to application databases is outside the scope of WS-Federation, as it focuses on authentication and identity management rather than direct data access or management.