How can organisations use API testing in identity reviews?

Why This Matters for Security Teams

API testing belongs in identity reviews because identity risk is not just about who can log in, but what an identity can actually do when it calls a service. Test results can expose over-permissive scopes, broken token validation, weak denial handling, and fallback paths that bypass intended controls. That makes API testing a practical evidence source for access certification, exception tracking, and remediation prioritisation, especially when service accounts and api key are involved.

This is particularly important in environments where secrets are hard to inventory. NHI Mgmt Group notes that only 5.7% of organisations have full visibility into their service accounts in the Ultimate Guide to NHIs, and that visibility gap turns identity reviews into guesswork. When reviewers can see how an identity behaves under test, they can validate policy against reality instead of relying on stale entitlement records. The same problem shows up in breach patterns documented in 52 NHI Breaches Analysis.

Used well, API testing gives security teams a repeatable way to confirm whether access is truly least privilege, whether errors leak useful information, and whether controls degrade safely. In practice, many security teams encounter excessive access only after a routine integration failure or incident response has already exposed it.

How It Works in Practice

Identity reviews usually focus on entitlements, owners, and rotation dates, but API testing adds behavioural evidence. During the review window, testers can call representative endpoints with known-good, expired, missing, or over-scoped credentials and record how the system responds. The goal is not penetration testing for its own sake. The goal is to verify that the observed access pattern matches the intended policy and that failures are explicit, logged, and enforced consistently.

A practical review often checks four things. First, whether the token or key is accepted only for the intended audience, issuer, and expiry. Second, whether privilege boundaries hold when the caller attempts a higher-risk action. Third, whether denial responses are clear enough to support operations without leaking sensitive detail. Fourth, whether the service falls back to a weaker path when primary identity checks fail. Guidance from the NIST Cybersecurity Framework 2.0 supports using evidence-based validation to strengthen governance and access control decisions.

Security teams can make this usable by mapping test cases to review questions such as:

• Does the API reject expired or revoked tokens immediately?
• Are service-to-service calls constrained to the minimum endpoint set?
• Do error messages avoid exposing identifiers, secrets, or internal policy logic?
• Are denied actions logged with enough context for access review?

For organisations building stronger NHI oversight, NHI Mgmt Group’s Top 10 NHI Issues is useful context because API behaviour often reveals the same root causes: excessive privilege, weak rotation, and poor visibility. These controls tend to break down when legacy services share credentials across environments because test results no longer reflect a single identity-to-resource relationship.

Common Variations and Edge Cases

Tighter API testing often increases review time and test maintenance, so organisations have to balance stronger evidence against operational overhead. That tradeoff is real, especially when services change frequently or when access reviews must complete on a fixed cadence. Current guidance suggests focusing on high-risk identities first, rather than trying to test every endpoint equally.

There is no universal standard for how much API testing is enough for an identity review. For stable internal services, a small set of repeatable tests may be sufficient. For customer-facing APIs, privileged automations, or third-party integrations, the review should be broader and should include negative testing and token lifecycle checks. Behavioural evidence becomes even more valuable when entitlements are incomplete, which is common in environments with many machine identities.

One common edge case is shared service accounts. If several systems use the same identity, the test results may confirm policy compliance at the API level while still leaving ownership and accountability ambiguous. Another is asynchronous or queued processing, where the initial API call appears to succeed but later background actions use a different privilege path. In those cases, API testing should be paired with log review and control exception tracking. The practical lesson from NHI breach research is that visible access is not always the same as safe access.

Related resources from NHI Mgmt Group

• How can organisations use standards work to improve identity security?
• When should organisations use reusable identity credentials instead of re-verifying users?
• How should organisations use data observability for AI reliability and audit readiness?
• How should security teams use DNS analytics in an identity programme?