Resolve CORS in complex SPAs by aligning API origins, preflight headers, credentials, and proxy rules-then log OPTIONS failures to pinpoint misconfigured gateways.

Fix bottlenecks by mapping vendor quotas, batching calls, adding adaptive retries, and caching repeat requests to keep third-party integrations reliable under rate limits.

Backward-compatible REST APIs preserve contracts: add optional fields, avoid changing meanings, version only for breaking changes, and document deprecations with clear timelines.

Implement OAuth 2.0 safely: use Authorization Code with PKCE, keep secrets server-side, rotate credentials, and never embed client secrets in mobile, SPA, or public code.

Top API pentest tools in 2026 pair OpenAPI-aware scanning, auth testing, fuzzing, and CI/CD integration to find exploitable flaws before attackers do.