Financial institutions should inventory every API, classify which ones handle sensitive data, and continuously compare the live environment against that inventory. The goal is to surface undocumented, outdated, and rogue APIs before they become exposure points. Discovery works best when it supports security, compliance, and decommissioning decisions, not just documentation. Without that baseline, teams cannot reliably govern access, data flow, or change risk.
How to design API discovery around real exposure, not just inventory
A useful API discovery programme starts with coverage, then adds meaning. Financial institutions need to find public, partner-facing, internal, and shadow APIs, but discovery only reduces blind spots when each API is classified by business owner, data sensitivity, authentication pattern, and whether it can change state or expose regulated data. The OWASP API Security Top 10 is a strong companion because discovery should immediately feed the kinds of checks that expose broken authorisation and excessive exposure, not stop at naming endpoints.
That baseline should be built from multiple signals, not a single scanner. API gateways, developer portals, code repositories, traffic telemetry, cloud logs, service catalogs, and external attack surface data each see a different slice of the estate. If one source is treated as authoritative, undocumented APIs, obsolete versions, and orphaned partner integrations can stay invisible long enough to create governance and breach risk.
Discovery also needs version and lifecycle context. An API that is technically reachable but no longer maintained can be more dangerous than a newer one because it often lacks ownership, logging, and a clear decommission path. For that reason, discovery is most valuable when it produces a living register that can be consumed by architecture, security testing, access governance, and retirement workflows. The NHI Lifecycle Management Guide is relevant here because the same operational discipline that supports inventory, ownership, and offboarding applies when APIs are treated as controlled assets rather than static records.
What good API discovery programmes measure and connect
The best programmes measure coverage gaps, stale records, and time to remediation rather than counting discovered endpoints alone. If the live estate is not continually compared against the register, the inventory becomes documentation drift, not control. Financial institutions should expect discovery output to answer practical questions such as which APIs handle customer data, which are externally exposed, which are authenticated, which are unauthenticated by design, and which have no clear owner.
Discovery also needs to connect to risk decisions. Some APIs may be acceptable because they are low sensitivity and tightly constrained; others should trigger immediate review because they expose payments, account data, trading workflows, or third-party access paths. That is why classification matters as much as enumeration. Once an API is tagged correctly, security teams can prioritise testing, access review, segmentation, and retirement based on actual exposure rather than organisational assumptions.
For financial services, this also supports compliance and change control. If discovery is tied to approvals and decommissioning, teams can detect when a new API appears outside normal release channels, when a partner integration has outlived its contract, or when an old endpoint remains live after a migration. The EU Digital Operational Resilience Act (DORA) is useful context for this operating model because financial institutions are expected to maintain stronger control over ICT dependencies, third-party exposure, and operational resilience.
Discovery is also where api security starts to overlap with broader identity and access governance. When an API is documented, the next question is usually who or what can call it, whether that access is least privilege, and whether partner or service credentials are still valid. That makes the The State of Non-Human Identity Security a useful reference point, because undocumented APIs often persist alongside unmanaged service credentials, weak visibility, and overexposed third-party access.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10 and OWASP Non-Human Identity Top 10 address the attack surface, CIS Controls v8 and NIST CSF 2.0 set the technical controls, and DORA define the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | A3 — API and Tool Abuse | APIs are attack surfaces where broken access and misuse create exposure. |
| Recommendation — Test API access paths for authorization and abuse paths before production release. | ||
| CIS Controls v8 | 6 — Access Control Management | Discovery should feed ownership, least privilege, and access review decisions for APIs. |
| 7 — Continuous Vulnerability Management | Discovery supports finding outdated or rogue APIs that require remediation or retirement. | |
| Recommendation — Inventory API access paths and revoke unused or unowned exposure promptly. Scan continuously for undocumented API assets and remove obsolete endpoints from service. | ||
| NIST CSF 2.0 | ID.AM — Asset Management | API discovery is fundamentally about identifying and maintaining an accurate asset inventory. |
| GV.OC — Organizational Context | API classification should reflect business criticality, data sensitivity, and regulatory impact. | |
| Recommendation — Maintain a living inventory of APIs and reconcile it against runtime reality. Classify APIs by business and data criticality to guide security prioritization. | ||
| DORA | ICT risk management — ICT Risk Management | Financial institutions need visibility into APIs as part of operational resilience and ICT control. |
| Recommendation — Map APIs into ICT risk processes and enforce ownership for each service. | ||
| OWASP Non-Human Identity Top 10 | NHI-01 — Discovery and Inventory | Undocumented APIs often coexist with unmanaged machine credentials and hidden access paths. |
| NHI-04 — Rotation and Expiration | API discovery often reveals stale integrations and credentials that should be retired or rotated. | |
| NHI-08 — Secrets Management | API discovery improves visibility into endpoints that depend on exposed keys or tokens. | |
| Recommendation — Discover all machine-facing access points and bind them to an owned inventory. Rotate or retire credentials tied to APIs that are no longer actively governed. Move API credentials into managed secrets workflows and eliminate hardcoded access. | ||
Practitioner Guidance
What to prioritise: Start with the APIs that can move money, expose customer data, or accept third-party traffic, then work outward to internal and low-risk services. Those are the endpoints where incomplete discovery most quickly turns into governance failure or breach impact.
What to verify: Make sure every discovered API has an owner, a data classification, a last-seen timestamp, and an operational status such as active, deprecated, or retired. If any of those fields are missing, the programme is not yet actionable enough to reduce blind spots.
Common mistake: Treating API discovery as a one-time scan. In practice, blind spots reappear through shadow deployments, version sprawl, partner integrations, and stale records unless discovery is continuously reconciled with runtime evidence.
Practitioner takeaway: A discovery programme only reduces exposure when it becomes a control loop, not a catalogue, meaning every new API, changed API, and retired API must change a security or governance decision.
Related resources from NHI Mgmt Group
- How should security teams build a third-party risk programme that actually reduces identity risk?
- How should security teams build a patch compliance programme that actually reduces risk?
- How should security teams build a phishing programme that actually reduces risk?
- How should security teams build a vulnerability testing programme that covers networks, applications, cloud, and databases without creating blind spots?
