API Security: A Practioner’s Approach

February 20th, 2026

What Are APIs And How Do They Factor Into An Organization’s Threat Landscape?

Application Programming Interfaces (APIs) allow for communication between systems by enabling the sharing of data and functions at defined endpoints. APIs are used to connect internal systems, power web/mobile apps, automate workflows, and expose selected capabilities to partners and third parties. In general, they underpin microservices and client-facing features (for example, retrieving account data or initiating payments), making it easier for associates to build and integrate services. APIs significantly expand an organization’s attack surface because every endpoint, method, and integration is a potential entry point, data exposure point, or abuse/misuse vector. APIs are susceptible to business logic abuse, DOS attacks, third-party exposure, injection, broken authentication, excessive data exposure, and much more.

Practical Controls To Secure APIs

Inventory and discovery:

• Maintain documentation that serves as a catalog of all APIs (external and internal), API consumers, exposure levels, etc.

• Continuously monitor traffic and conduct code security reviews and scanning to find shadow/rogue/orphan endpoints.

Strong authentication and Fine-grained authorization:

• Prefer OAuth2/OIDC with short-lived tokens, refresh tokens where appropriate, and scope/audience constraints.

• Validate JWTs (issuer, audience, expiration, signature); consider token-binding or DPoP for public clients.

• Enforce object-level checks on every read/update/delete call.

• Implement role-based or attribute-based access control with least privilege and per-tenant isolation.

• Separate read vs. write endpoints and minimize privileged operations.

Rate limiting and abuse prevention:

• Apply per-client/token/IP rate limits and quotas; add burst controls and detection for unusual patterns.

• Consider bot/bot-management measures on public endpoints, like throttling heavy queries.

Input/output discipline:

• Enforce strict schemas; validate types, ranges, and formats; reject unknown fields to prevent mass assignment.

• Minimize response payloads to only required fields; avoid leaking internal identifiers or PII.

• Sanitize error messages; avoid verbose stack traces in responses.

Secure transport and client-side considerations:

• Enforce TLS everywhere with the correct TLS versions/ciphers.

• Use mTLS internally; lock down CORS to known origins and methods.

• Avoid putting secrets in client-side code; never expose API keys to browsers.

Secrets management:

• Store and rotate API keys/certs in a secrets vault; avoid hardcoding in code or configs.

Logging, monitoring, and detection:

• Use structured logs with correlation IDs; centralize logs into a SIEM and alert on auth failures, abnormal rates, and sensitive resource access.

Testing and assurance:

• SAST/DAST focused on APIs, fuzzing and negative tests, contract tests, and regular penetration tests.

• Threat modeling for new endpoints; red-teaming of high-risk workflows such as payments and transfers.

Additional Considerations

• Client-facing APIs are prime targets for credential stuffing, business logic abuse, and data exposure. Ensure rate limits, strong auth, and minimal data return.

• Internal microservice APIs still matter; a compromise inside the network can pivot through east–west calls, so maintain mTLS, per-service authentication, and segmentation.

• Mobile and browser clients: Mobile apps can leak endpoints or keys; browser-based flows require special care for CORS, CSRF (for state-changing operations), and OAuth. Protect against reverse engineering; use dynamic client attestation if appropriate and never embed secrets.

The Bottom Line

APIs are the front door to an organization’s digital business. If they are not properly secured, a single call can expose client data, enable fraud, disrupt services, and trigger regulatory and reputational damage. Strong API security protects client trust, revenue, and operational resilience, letting the organization integrate and optimize operations confidently without turning convenience into risk.

— Ben Skinner