How should security teams combine FIDO2 and PKI without creating overlap?

Why This Matters for Security Teams

FIDO2 and PKI are often treated as competing identity strategies, but they solve different trust problems. FIDO2 is designed for phishing-resistant human authentication, while PKI underpins machine identity, signed documents, email trust, and encryption workflows. When teams blur that boundary, they create duplicate controls, unclear ownership, and brittle exception paths that are hard to audit and even harder to rotate.

That overlap becomes costly when security and platform teams both assume they own identity proofing, lifecycle management, or revocation. NHI Management Group’s Ultimate Guide to NHIs notes that 71% of NHIs are not rotated within recommended time frames, which is exactly the kind of operational drift that appears when certificate and authenticator governance is mixed together. For human authentication guidance, NIST SP 800-63 Digital Identity Guidelines keeps the human identity problem in scope rather than forcing machines into the same control model.

In practice, many security teams discover the overlap only after certificates, passkeys, and service credentials have already been grouped into one lifecycle process, rather than through intentional design.

How It Works in Practice

The cleanest approach is to assign FIDO2 to people and PKI to non-human workflows, then build separate governance paths that still report into the same risk and inventory model. FIDO2 authenticators, including passkeys and security keys, should be managed as human factors tied to enrollment, recovery, and phishing-resistant login. PKI should manage certificates for workloads, devices, email, code signing, document signing, and encryption trust chains.

That split matters because the failure modes are different. FIDO2 credentials are bound to a user’s authentication event and are not meant to represent a service, API client, or autonomous workload. PKI identities, by contrast, are often consumed by systems that need cryptographic proof of identity at machine speed and with automated renewal. The operational goal is not to make the two systems behave alike, but to coordinate their inventories, ownership, and revocation.

• Use FIDO2 for interactive human sign-in and privileged admin access.
• Use PKI for machine identity, mutual TLS, signing, and encryption.
• Keep separate issuers, renewal rules, and revocation workflows.
• Map both to a common asset and owner inventory for auditability.
• Apply policy-by-context so the wrong identity type cannot be used in the wrong workflow.

This is where NHI discipline helps. The NHI Management Group Ultimate Guide to NHIs emphasizes lifecycle control, rotation, and offboarding for non-human identities, which aligns well with PKI certificate automation but not with human authenticator handling. For certificate and trust infrastructure, the current guidance from NIST SP 800-63 Digital Identity Guidelines reinforces that authentication assurance should be matched to identity type and use case rather than merged into a single control plane.

These controls tend to break down when legacy applications expect one shared certificate store for both users and services, because revocation, renewal, and recovery events then become indistinguishable across identity classes.

Common Variations and Edge Cases

Tighter separation often increases operational overhead, requiring organisations to balance cleaner trust boundaries against the cost of running two lifecycle models. The tradeoff is worth it, but there are edge cases where the lines blur and current guidance suggests documenting them explicitly rather than improvising.

Shared kiosk environments, device enrollment, and SSO recovery flows can create temporary intersections between FIDO2 and PKI. In those cases, best practice is evolving: the human authenticator should still prove the user, while PKI should issue only the machine or device certificate needed for the task. There is no universal standard for collapsing those identities into one artifact, and doing so usually creates audit ambiguity.

Teams should be especially careful where certificate authorities, IAM platforms, and secrets management all touch the same provisioning pipeline. Use separate approvals, separate expiration logic, and separate incident response runbooks. That reduces the chance that a human recovery event accidentally renews a machine certificate, or that a workload certificate is treated like a user login factor. For broader NHI context, The State of Non-Human Identity Security shows how quickly visibility gaps appear once non-human trust is left to ad hoc processes, especially in environments with many third-party connections.

When platforms merge authenticator and certificate governance to simplify procurement, they often create the exact overlap they were trying to avoid.

Related resources from NHI Mgmt Group

• How should security teams use FIDO2 without creating blind spots in IAM?
• How should security teams authenticate AI agents in enterprise environments?
• How should security teams use AI in secret scanning without creating new blind spots?
• How should security teams implement Client ID Metadata Documents?