🛡️ Sentinel: [security improvement] Add HTTP security headers

[google-labs-jules]

🛡️ Sentinel Report

Security Enhancement: Added standard HTTP security headers to protect against common web vulnerabilities.

Changes:

• Added X-Content-Type-Options: nosniff to prevent MIME type sniffing.
• Added X-Frame-Options: DENY to prevent clickjacking.
• Added Content-Security-Policy: default-src 'none'; frame-ancestors 'none' to mitigate XSS and other injection attacks.
• Added verification test in src/http-transport-security.test.ts.

Verification:

• Ran npm test src/http-transport-security.test.ts to verify headers are present.
• Headers are applied before other middleware to ensure coverage even for early errors.

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PR created automatically by Jules for task 2995640537602651643 started by @davidruzicka

[google-labs-jules]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!

[davidruzicka]

This is not a web application and it does not run in a browser. What exactly are these added security HTTP headers used for?

[google-labs-jules]

This is not a web application and it does not run in a browser. What exactly are these added security HTTP headers used for?

Valid question. While this is primarily an API server, the HTTP transport includes OAuth endpoints (/oauth/authorize, /oauth/callback) which are accessed via a browser during the authentication flow. These headers provide Defense in Depth:

1. X-Content-Type-Options: nosniff: Prevents browsers from incorrectly detecting non-script responses as scripts (MIME confusion).
2. X-Frame-Options: DENY: Prevents clickjacking attacks on any present or future browser-facing endpoints.
3. Content-Security-Policy: Mitigates potential XSS risks if an error message or response is ever rendered as HTML by a browser.

Adding these headers is a low-cost, standard security best practice that protects against edge cases without affecting API clients.