正解:C
Federation is a technology that allows a social media application to authenticate access to resources that are available in the cloud. Federation enables users to sign in to a cloud service using their existing credentials from another identity provider, such as Facebook, Google, or Microsoft. This way, users do not need to create a separate account or password for the cloud service, and the cloud service does not need to store or manage user identities. Federation also simplifies access management, as the identity provider can control which users and groups are allowed to access the cloud service. Federation is based on standards such as OAuth, OpenID Connect, and SAML, which define how identity providers and cloud services can exchange authentication and authorization information.