Treat the flow as machine identity governance, not just authentication plumbing. Require named ownership, protected private key storage, separate review of refresh rights, and a revocation path for both the token and the key when the integration changes. If the API can renew access on its own, that renewal path must be governed like any other privileged entitlement.
Why This Matters for Security Teams
Signed challenges and refresh tokens can look like simple API plumbing, but they create a machine identity lifecycle that security teams must govern. The risk is not just whether the initial authentication succeeds. The real exposure is whether the private key, signing path, and refresh grant can be abused after the original integration changes, is cloned, or is abandoned. That is why this belongs in identity governance, not only application engineering.
Current guidance from the NIST Cybersecurity Framework 2.0 supports treating authentication assets as managed risk objects with ownership, review, and revocation. NHIMG research shows why this matters in practice: in the 2025 State of NHIs and Secrets in Cybersecurity, 91% of former employee tokens remained active after offboarding, showing that lifecycle gaps outlive the original user or system.
In practice, many security teams encounter token misuse only after the integration has already been repurposed, rather than through intentional review of who can renew access and why.
How It Works in Practice
A signed-challenge flow usually proves possession of a private key, while a refresh token extends access without repeating the full authentication ceremony. Security teams should govern these as two related but distinct entitlements: key custody and renewal authority. The private key proves the workload, service, or application is the right machine identity. The refresh token proves it may continue operating over time. Both need ownership, logging, and a revocation path.
For stronger control, align the design to machine identity principles described in the Top 10 NHI Issues and the broader identity lifecycle practices in Guide to the Secret Sprawl Challenge. Pair that with the NIST Cybersecurity Framework 2.0 by mapping the integration to an owner, a data classification, and a renewal review cadence.
- Store the signing key in protected hardware or a managed secret store, not in code, tickets, or shared documents.
- Issue refresh tokens with narrow scope and short lifetime, and rotate them when the application, environment, or vendor trust changes.
- Separate approval for initial access from approval for refresh rights, because renewal is an ongoing privilege.
- Record which service owns the token, which system issued it, and which process can revoke it.
- Test revocation for both the token and the key, because one without the other leaves a gap.
If the API can renew access automatically, the renewal path should be treated as a privileged entitlement and evaluated whenever the workload, owner, or upstream trust boundary changes.
Common Variations and Edge Cases
Tighter token controls often increase operational overhead, requiring organisations to balance service reliability against revocation speed and key rotation frequency. Best practice is evolving for clustered services, delegated integrations, and vendor-managed APIs, so there is no universal standard for every case yet. The practical question is whether the refresh path can be constrained without breaking legitimate automation.
One common edge case is service-to-service delegation, where a backend system refreshes on behalf of many downstream jobs. That pattern can hide excessive privilege if the refresh token is shared across applications. Another is long-lived enterprise integrations, where teams keep refresh tokens alive because reauthorisation is inconvenient. NHIMG incidents such as the Salesloft OAuth token breach and the Dropbox Sign breach show how durable API trust can become a blast-radius problem when renewal or third-party access is not aggressively scoped.
Where this guidance breaks down most often is in legacy systems that cannot separate signing authority from refresh authority, because revocation then becomes all-or-nothing and operations teams resist timely rotation.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 and CSA MAESTRO address the attack and risk surface, while NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-03 | Refresh tokens need lifecycle control and timely rotation, which this control addresses. |
| NIST CSF 2.0 | PR.AC-1 | Machine authentication must tie to named ownership and managed access decisions. |
| CSA MAESTRO | ID-2 | Agent and workload identities require governed issuance and renewal paths. |
Treat refresh tokens and signing keys as governed workload identities with explicit issuance and revocation.
Related resources from NHI Mgmt Group
- How should security teams govern API keys used for generative AI access?
- How should security teams govern authentication in hybrid Active Directory and cloud identity environments?
- How should security teams govern non-human identities at scale?
- How should security teams govern non-human identities for compliance?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on July 8, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
