A federated identity solution is a system that allows users to access multiple services or applications across different domains or organizations using a single identity and credential. A federated identity solution involves two main parties: the Identity Provider (IdP) and the Service Provider (SP). The IdP is the party that verifies the identity and credential of the user and issues a security token or assertion to the user. The SP is the party that provides the service or application that the user wants to access and relies on the security token or assertion from the IdP. Therefore, the primary responsibility of the IdP in a federated identity solution is authentication, which is the process of verifying the identity and credential of the user. Access control, account management, and authorization are not the primary responsibilities of the IdP, as they are more related to the SP or the user's own organization. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 15:
Identity and Access Management, page 901; CISSP Official (ISC)2 Practice Tests, Third Edition, Domain 5:
Identity and Access Management, Question 5.4, page 218.