Authentication and Authorization Testing

API authentication testing requires understanding various token-based mechanisms. Bearer token testing involves analyzing JWT (JSON Web Token) structures for weak signatures, algorithm confusion attacks, or sensitive data in payloads. Use ZAP's proxy to capture tokens, then decode and analyze them. Test token expiration, refresh mechanisms, and revocation handling. Weak implementations might accept expired tokens or fail to validate signatures properly.

Authorization testing in APIs focuses on horizontal and vertical privilege escalation. Horizontal escalation involves accessing other users' resources by manipulating identifiers. Capture requests for your own resources, then modify user IDs, account numbers, or resource identifiers to attempt accessing other users' data. Vertical escalation attempts to perform administrative actions with regular user credentials. Test by replaying administrative requests with lower-privileged tokens.

API key security assessment examines how applications handle authentication keys. Test whether API keys are transmitted securely, properly scoped to specific operations, and regularly rotated. Look for API keys in client-side code, mobile applications, or public repositories. ZAP's passive scanner identifies potential API keys in responses. Test key revocation by using old keys and observing whether they're properly rejected.