A Comparative Review of Cloud Identity and Access Management Architectures Using Zero-Trust, Decentralized Identity, and AI-Based Techniques

: Cloud Identity and Access Management (IAM) has become a central pillar of cloud security, governing authentication, authorization, and identity lifecycle management across increasingly complex cloud ecosystems. This review provides an in-depth examination of contemporary Cloud IAM architectures, the expanding identity attack surface in multi-cloud and distributed environments, and the operational challenges arising from scale, heterogeneity, and dynamic access requirements. It synthesizes recent research on access control models, Zero-Trust architectures, self-sovereign and decentralized identity frameworks, and AI-assisted IAM mechanisms for anomaly detection, adaptive authentication, and policy enforcement. The review further analyses empirical and conceptual studies addressing cross-cloud interoperability, CIAM – PAM integration, privacy-preserving identity management for IoT and constrained devices, and formal verification of access control policies.