Why do critical infrastructure environments need identity-centric defences for Zero Trust?

Why Identity-Centric Defences Matter in Critical Infrastructure

Critical infrastructure is not protected by a clean perimeter anymore. Operators rely on cloud services, service accounts, APIs, OT gateways, recovery tooling, and vendor integrations that all authenticate independently. That creates a simple failure pattern: if identity is weak, zero trust becomes a slogan rather than an operating model. NHI Management Group research shows that 90% of IT leaders say properly managing NHIs is essential for successful zero-trust implementation, which tracks with what defenders see in the field: excessive privilege and stale secrets usually outlast perimeter controls. The NIST view of Zero Trust reinforces this shift by treating every access request as untrusted until verified by context and policy, not network location alone, as outlined in NIST SP 800-207 Zero Trust Architecture.

For infrastructure operators, the real risk is that the same identity layer often spans business IT and operational technology. A compromised API key can become a path into scheduling, telemetry, patching, or recovery workflows. NHIMG’s Ultimate Guide to NHIs explains why visibility, rotation, and offboarding matter as much as authentication itself. In practice, many security teams discover identity-driven lateral movement only after a service account has already been used to bridge from one trusted segment to another.

How Identity-Centric Zero Trust Works in Practice

Identity-centric defence starts by treating every workload, service account, certificate, and agent as a distinct subject with its own lifecycle. The goal is to replace broad network trust with runtime checks that ask: what is this identity, what is it trying to do, and should it be allowed right now? For critical infrastructure, that means binding access to workload identity, device posture, location, purpose, and policy rather than assuming a session is safe because it originated inside a trusted zone.

Current guidance suggests four practical controls:

• Use strong workload identity and short-lived credentials so access is issued per task, not left standing for months.
• Apply least privilege with explicit scoping for OT, IT, and recovery systems so a single credential cannot roam across domains.
• Continuously evaluate policy at request time rather than relying on static allow lists that age poorly.
• Log and review identity events across humans and non-humans so anomalous use of secrets is visible before it becomes an outage.

That operational model is supported by NHI-focused guidance in Guide to SPIFFE and SPIRE, which is useful when teams need cryptographic proof of workload identity instead of static credentials alone. It also aligns with threat reporting from CISA cyber threat advisories, where credential abuse remains a persistent attack path. These controls tend to break down in brownfield environments where legacy PLCs, vendor remote access, and fixed-function OT appliances cannot support modern token exchange or continuous policy checks.

Common Variations and Edge Cases

Tighter identity controls often increase operational overhead, so organisations must balance resilience against deployment complexity. In practice, the hardest environments are not the most modern ones, but the mixed estates where older OT assets, regulated change windows, and third-party maintenance access all coexist. Best practice is evolving here: there is no universal standard for how aggressively to retrofit Zero Trust into legacy control systems, especially where availability and safety take precedence over perfect segmentation.

One common edge case is vendor access. A partner may need emergency visibility into a turbine controller, a SCADA historian, or a maintenance scheduler, but standing access is exactly what Zero Trust tries to eliminate. Another is recovery tooling, where break-glass accounts and backup paths are often exempted from normal controls. Those exceptions are sometimes necessary, but they should be time-bound, heavily monitored, and separated from routine operational access. NHIMG’s 52 NHI Breaches Analysis shows why this matters: the highest-impact incidents often begin with non-human credentials that were over-privileged, poorly rotated, or left valid long after they should have expired.

For critical infrastructure, identity-centric Zero Trust is less about blocking everything and more about making every exception explicit, temporary, and auditable. That is the practical difference between policy on paper and control in the real world.

Related resources from NHI Mgmt Group

• How should security teams implement identity controls as they move toward zero trust in cloud environments?
• How should security teams implement shared signals in zero trust identity architectures?
• How should identity, endpoint, and security platforms share risk signals in a zero trust model?
• How should security teams implement zero trust architecture in environments with remote users and non-traditional mission partners?