Replace CSRF cookie with CrossOriginProtection

[silverwind]

Removes the CSRF cookie in favor of CrossOriginProtection which relies purely on HTTP headers.

Fixes: #11188
Fixes: #30333
Helps: #35107

TODOs:

• Fix tests
• Ideally add tests to validates the protection

[silverwind]

Test failures need investigation. I think I was quite thorough with this removal, rg csrf returns clean.

[silverwind]

Unexpectedly, the fix in 1eb058d worked to fix the last issue. I think there may be a underlying bug why this test is sensitive to a GET request, but as far as this PR is concerned, its ok.

[lunny]

Maybe use a new test for CrossOriginProtection

[silverwind]

Yes I would still like to add a integration test that leverages Sec-Fetch-Site to validate this protection.

[wxiaoguang]

⚠️ BREAKING ⚠️

The _crsf cookie will no longer be set and is no longer necessary to be sent. GET requests that were used to retrieve it are no longer neccessary.

"breaking" usually means end users or site admins must do something, or experience something totally different.

But for this one, I think it isn't really "breaking". WDYT?

---

And, the TODOs are not necessary (or, we shouldn't "add additional trusted origins", there is no such use case)

[silverwind]

I think the cors handler could indicate in the request context that it had a match with a boolean flag, and then the COP handler could act on that flag and be disabled.

[silverwind]

I'm not sure your AI answer is right. Go's protection relies on Sec-Fetch-Site or Origin headers and I think one, if not both headers will be present on CORS request, at least for the unsafe methods. There is even a Sec-Fetch-Mode: cors, which further reinforces my assumption.

So I'd lean towards having all endpoints protected, without exception. Restrictions can be relaxed later if issues are demonstrated. I will push again the full strict settings.

[wxiaoguang]

I'm not sure your AI answer is right.

AI's answer is right, I asked a general question.

Go's protection relies on Sec-Fetch-Site or Origin headers and I think one, if not both headers will be present on CORS request, at least for the unsafe methods.

That's Golang's implementation. And you MUST make CrossOriginProtection work with CORS config, but not just make a new default CrossOriginProtection.

[silverwind]

I don't mind having unprotected CORS routes but that AI answer seems nonsensical to me:

If your server implements a policy that rejects Sec-Fetch-Site: cross-site for certain endpoints, the server can block it (e.g., respond 403) even if CORS would otherwise allow it.

My understanding is that all requests, including CORS preflights will send one of Sec-Fetch-Site or Origin and when I ask google ai, it confirms this:

[wxiaoguang]

That's Golang's implementation. And you MUST make CrossOriginProtection work with CORS config, but not just make a new default CrossOriginProtection.

See my comment above. "CrossOriginProtection" must accept (trust) that origin, if I understand correctly.

[silverwind]

I've read a bit more on these topics, these seem like good resources:

https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html
https://www.alexedwards.net/blog/preventing-csrf-in-go

From what I gather, these header checks alone are not recommended, but header checks combined with a SameSite cookie (lax or strict) is recommended as adequate protection.