Turn API security assumptions into repeatable checks

Map the trust boundaries

List where untrusted information enters the system and where it can influence a protected resource. Include path identifiers, query parameters, request bodies, uploaded references, and data returned by another API. Identify the checks that must happen before an operation reads or changes state.

The OWASP API Security Top 10 includes object-level authorization, authentication, resource consumption, inventory management, and unsafe consumption of external APIs. Use these categories to organize questions, then adapt the actual tests to your application.

Write checks around expected access

Create a permission matrix with roles on one axis and operations or resource types on the other. Include access to another user’s test record, restricted properties, and privileged functions. Perform these checks only in an authorized environment using controlled accounts and data.

• Identity: How are missing, expired, or revoked credentials handled?
• Authorization: Does access depend on the specific record and requested action?
• Input: Are size, type, range, and allowed fields validated?
• Consumption: Are costly operations bounded and external results treated cautiously?

Check what the response reveals as well as whether the operation succeeds. A denied operation can still disclose sensitive fields through verbose errors, debug information, or unexpected response properties.

Maintain an accurate surface map

Keep an inventory of deployed hosts, versions, and operations. Compare documentation with what your authorized environment exposes. Old debug routes and forgotten versions deserve an owner and an explicit decision about whether they should remain available.

Record each check with its preconditions, expected result, observed result, and affected version. Redact credentials and unnecessary personal information from evidence. Give confirmed issues an owner and a retest condition.

Automate stable regression checks where they protect a meaningful boundary. Use deeper manual investigation when a workflow’s business logic cannot be captured by a simple request assertion. A passing test set describes what was checked; it is not a universal guarantee.

Use penetration-test scoping for a focused adversarial assessment. The MCP guide applies the same access questions to model-connected tools and resources.