AWS IAM Explained: Zero-Trust Access Control for Cloud Infrastructure

AWS Identity and Access Management (IAM) serves as the central security control plane for managing authentication and authorization across all AWS cloud resources. It enforces a default-deny model, meaning every API request is blocked unless explicitly permitted by a matching policy. IAM supports multiple identity types — individual users, groups, and roles — with roles being preferred for workloads as they issue short-lived credentials via the AWS Security Token Service, limiting exposure if compromised. Policies are JSON documents specifying allowed or denied actions on specific resources, with explicit denies always overriding any allow statements. Access decisions pass through a layered evaluation chain that includes Service Control Policies, resource-based policies, identity-based policies, and permission boundaries before access is granted or denied.