When do passkey-based signatures become more appropriate than backend signing infrastructure?

Why This Matters for Security Teams

Passkey-based signatures are not just a UX choice. They change where trust lives. Instead of concentrating signing risk in backend infrastructure, they can shift assurance toward a user- or agent-held authenticator with cryptographic proof. That becomes attractive when the organisation needs portable signing, lower operational overhead, and a cleaner path for workflows that span browsers, endpoints, and managed devices. The security question is whether the assurance model fits the signing event, not whether the cryptography is modern.

For non-human identities, the core issue is governance. If a workload can sign from many environments, backend-only controls may become brittle, especially when long-lived secrets are involved. NHIMG research shows that 80% of identity breaches involved compromised non-human identities such as service accounts and API keys in the Ultimate Guide to NHIs, which is why teams increasingly look for signing approaches that reduce secret sprawl. NIST’s NIST SP 800-53 Rev 5 Security and Privacy Controls remains useful here because the control objective is still accountability, traceability, and least privilege. In practice, many teams discover the weakness only after backend signing keys have already become a high-value target rather than through intentional design.

How It Works in Practice

Passkey-based signatures become more appropriate when the signer can authenticate with a phishing-resistant, device-bound credential and the workflow can tolerate user or agent presence at the point of signing. For humans, that usually means a passkey-backed approval or transaction-signing flow. For agents, the emerging pattern is to separate the agent’s workload identity from the signing act itself, so the agent can request a signature but cannot silently mint one without policy checks.

That distinction matters because backend signing infrastructure often centralises too much power. It can be strong for high-volume machine signing, but it also creates a durable key-management burden, a larger blast radius, and a dependency on tightly secured service paths. Passkeys reduce that burden by using device-held authenticators and attested user presence or verification. Where this is implemented well, the signing event is bound to context: who requested it, what was being signed, which device or agent initiated it, and whether the action satisfies policy at runtime.

In agentic workflows, the best practice is evolving toward runtime authorisation rather than static permission sets. That aligns with guidance from The 2026 Infrastructure Identity Survey, which found that 67% of organisations still rely heavily on static credentials despite the risks they pose to agentic AI deployments. In parallel, standards such as FIDO passkey architecture and policy enforcement at request time help ensure that the signing action is ephemeral, attributable, and revocable. The operational question is not simply “can it sign?” but “can it sign only when the policy, device, and task context all line up?” These controls tend to break down in unattended backend batch systems because passkey-based approval assumes an available authenticator and an interactive trust event.

Common Variations and Edge Cases

Tighter signing controls often increase operational friction, so organisations have to balance assurance against throughput. That trade-off becomes obvious in high-volume service workflows, regulated approval chains, and autonomous systems that need to sign without a human in the loop.

There is no universal standard for this yet, but current guidance suggests three common edge cases. First, pure machine-to-machine signing still often fits backend infrastructure better when the signer is a non-interactive workload and the controls focus on HSM-backed key protection, rotation, and separation of duties. Second, passkey-based signing is more compelling when a human approves an action that an agent prepared, because the passkey can preserve user presence and reduce secret exposure. Third, mixed human-agent workflows may need both: a workload identity for the agent and a passkey step for final approval.

NHIMG’s research on TruffleNet BEC Attack - Stolen AWS Credentials illustrates why long-lived backend credentials remain attractive to attackers. The practical rule is simple: use passkey-based signatures when the signing event benefits from strong interactive assurance and portability, and keep backend signing for cases where automation, scale, or non-interactive execution outweigh those benefits. The pattern becomes fragile when organisations try to force passkeys into fully unattended pipelines, because the authenticator requirement collides with continuous machine execution.

Related resources from NHI Mgmt Group

• When does a machine identity become a compliance problem?
• When does secret exposure become a broader identity risk?
• What is the difference between role-based access and API key governance for NHI security?
• When does NHI compliance become an operational security issue?