Configures policy-as-code testing using OPA / Conftest / Cedar - authors policies in Rego (OPA's language), runs Conftest against Kubernetes manifests / Terraform plans / Dockerfiles / arbitrary structured data, integrates with CI for PR-time policy gates. Per OPA's docs: "an open source, general-purpose policy engine that unifies policy enforcement across the stack." Use to express + enforce custom policies (cost limits, tagging requirements, security baselines) that Checkov / tfsec / KICS don't cover.