Which service essentially governs how users authenticate across different domains?

The service that governs how users authenticate across different domains is the Federation of Identity Management (FIdM). This approach enables a single user identity to be used across multiple distinct domains, allowing for seamless access to various services and applications without the need for separate credentials in each domain.

FIdM employs standards such as SAML (Security Assertion Markup Language) and OAuth to facilitate this kind of cross-domain authentication. By establishing trust relationships between identity providers and service providers, FIdM allows users to authenticate once and gain access to multiple resources, significantly enhancing user experience and operational efficiency in distributed environments.

The other options do not accurately describe services related to cross-domain user authentication. Cross-Domain Connections refer to the technical pathways that allow data exchange between different domains but do not inherently manage authentication processes. Peer-to-Peer Segmentation involves organizing networks into smaller segments for security or performance benefits and is unrelated to user authentication. Software-Defined Networking focuses on the network management aspect and does not directly address the needs of identity and access management across multiple domains.