Access control is correct. Federation is primarily about enabling identities to be asserted across trust boundaries so that systems can make authentication and authorization decisions without creating separate local accounts.

Federation allows an identity provider to assert a user identity and related attributes to a service provider or relying party so access policies can be applied. This supports single sign on and delegated identity which are central to Access control because roles and permissions are granted based on the asserted identity and claims.

Tenant isolation is incorrect because that term refers to the logical separation of customer environments within a multi tenant cloud rather than the sharing of identity or trust between domains. Federation is about identity and trust not isolation mechanisms.

Multivendor network diversity is incorrect because it describes using equipment from multiple vendors for resilience or interoperability. Federation does not concern physical network vendor diversity and it does not manage network paths or devices.

Data center environmental systems is incorrect because that area covers cooling power and fire suppression and other physical controls. Federation is unrelated to environmental systems and instead deals with identity federation for authentication and authorization.

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