API keys and client secrets create risk because they are shared secrets, often stored poorly, and can be reused by anyone who obtains them. Once exposed, they may allow impersonation, unauthorized access, token replay, and unexpected usage costs. They also scale badly across distributed teams and third-party integrations, where visibility and rotation are often weak.
Why API Keys and OAuth Client Secrets Carry Outsized Risk
API keys and oauth client secret are dangerous because they are bearer-style or bearer-adjacent credentials: whoever possesses them can often act as the application, not just access it. That makes the secret itself the control boundary. When these values leak into code, CI logs, chat tools, or vendor handoffs, the attacker does not need to break encryption or defeat a password reset flow. They only need a usable copy of the secret.
The practical problem is that modern API estates spread these secrets across many systems and teams. A key may exist in source control, a deployment pipeline, a ticketing system, and a runtime environment at the same time, which multiplies exposure and makes revocation harder to coordinate. NHI Management Group research on secret sprawl shows that the State of Secrets Sprawl 2026 found 64% of valid secrets leaked in 2022 are still valid and exploitable today, a sign that discovery without rotation leaves organisations exposed.
In practice, many teams only discover the risk after a secret has been copied into a place they do not monitor and is already being used elsewhere.
How These Secrets Behave in Real Systems
API keys usually identify an application or integration, while oauth client secrets help authenticate the client during token exchange or related flows. In both cases, the risk is not theoretical possession of a string but the authority attached to it. If the secret is long-lived, widely shared, or reused across environments, the blast radius grows quickly because one exposure can unlock multiple services or data paths.
That risk is amplified by the way teams operationalise API access. Secrets are often embedded in configuration files, injected into build jobs, stored in vaults with weak governance, or passed through support channels during troubleshooting. The more systems that can see the secret, the more likely it is to be leaked, duplicated, or left active after the original use case has changed. Guidance from the OWASP Non-Human Identity Top 10 is especially relevant here because the core failure is usually not authentication theory, but lifecycle control over machine credentials.
- Short-lived credentials reduce the usefulness of a leak, while static secrets create durable reuse risk.
- Rotation only works when applications can accept a new secret without manual drift across environments.
- Least privilege matters because many API keys are over-scoped for convenience and then reused in ways nobody planned.
- Visibility must include code, logs, tickets, chat, and CI artifacts, not just vault inventory.
Practitioners should also distinguish between a secret that enables API access and a secret that can mint tokens with broader downstream authority, because the latter often creates a larger and less visible trust boundary. These controls tend to break down when teams treat every integration secret as a one-off configuration value rather than as a credential with its own lifecycle and revocation requirements.
Where the Risk Changes Shape
Tighter secret governance often increases operational overhead, so organisations have to balance speed of integration against blast-radius containment. The same pattern does not behave identically in every environment: a low-privilege sandbox key is not the same risk as a production OAuth client secret tied to customer data, billing, or privileged automation.
One important edge case is secret duplication. When the same credential is copied into multiple applications, environments, or vendor tools, compromise of any one location can expose the rest. Another is offboarding and system decommissioning. A secret can remain technically valid long after the team believes it has been retired, which makes stale inventory a real exposure rather than an administrative issue. NHIMG research on 17,000+ Secrets Exposed in Public GitLab Repositories is useful here because it shows how quickly routine development workflows can turn into credential exposure if secret handling is not engineered into the pipeline.
Best practice is evolving toward ephemeral credentials, workload identity, and automated revocation, but there is no universal standard for every API pattern yet. The right answer depends on whether the secret is for human-initiated support, machine-to-machine automation, or third-party access that cannot safely rely on a static shared secret.
Risk and Threat Considerations
API keys and OAuth client secrets create a direct impersonation risk because they frequently function as the application’s proof of identity. Once exposed, an attacker or unauthorised third party can use them to access APIs, enumerate data, trigger costly actions, or mint additional tokens where the client secret is part of a token exchange flow.
Failure mechanism: The common mechanism is secret exfiltration through code repositories, CI logs, chat tools, support tickets, endpoint compromise, or vendor integrations, followed by replay from an external system that looks legitimate to the target API. When the secret is static or overused, detection may arrive after the credential has already been copied into multiple places.
Impact: The consequence is not just access loss but trust collapse: unauthorized API calls, data exposure, service abuse, inflated usage costs, and a broader revocation problem because the same secret may underpin several systems or environments.
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 MITRE ATT&CK address the attack and risk surface, while CIS Controls v8, NIST CSF 2.0 and NIST AI RMF set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-01 — Secrets and Credential Management | API keys and client secrets are machine credentials with exposure and lifecycle risk. |
| Recommendation — Inventory, rotate, and revoke machine secrets before they can be reused. | ||
| CIS Controls v8 | 5 — Account Management | Shared API credentials need controlled assignment, review, and deprovisioning. |
| Recommendation — Remove stale credential access and verify ownership during offboarding and change. | ||
| NIST CSF 2.0 | PR.AA-01 — Identity Management, Authentication, and Access Control | API keys and client secrets are authentication artifacts needing access governance. |
| Recommendation — Enforce least-privilege authentication and limit each secret to its intended scope. | ||
| MITRE ATT&CK | T1552 — Unsecured Credentials | Exposed API keys and client secrets are a credential-access target for attackers. |
| Recommendation — Hunt for exposed secrets in code, logs, and collaboration tools and rotate them. | ||
| NIST AI RMF | GOVERN — Govern, Map, Measure, and Manage | Secret sprawl in API and automation workflows needs formal AI-era risk governance. |
| Recommendation — Set ownership, monitoring, and response expectations for all machine secrets. | ||
Practitioner Guidance
What to prioritise: Treat any API key or OAuth client secret that can reach production data, customer workflows, or automation as a high-value credential, not a configuration string. Prioritise secrets that are shared across environments, embedded in CI/CD, or reused by multiple applications because those conditions expand blast radius fastest.
What to verify: Confirm whether the secret is still needed, where it is stored, who or what can read it, and whether the application can move to rotation-friendly or short-lived authentication. If a secret cannot be revoked quickly without breaking production, that is an operational design issue, not just a security weakness.
Practitioner takeaway: The real control problem is not secret discovery alone; it is ensuring that every secret has a bounded lifetime, a clear owner, and a revocation path that still works when the secret is already suspected of exposure.
Related resources from NHI Mgmt Group
- Why do long-lived API keys create more risk than scoped OAuth 2.0 client credentials for machine-to-machine access?
- Why do service accounts and API keys create so much supply chain risk?
- Why do static client secrets create so much risk in workload authentication?
- Why do static SSH keys and API tokens create so much risk?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 9, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
