Are you sure about this? It's been a year or so since I've used it, but I remember being able to disable a lot of specific performance/caching stuff (where the CDN comes in) via its Page Rules and "Cache Level - Bypass": https://developers.cloudflare.com/support/page-rules/underst...
Date: <current server timestamp>
Original-Date: <same as Date>
This resulted in a considerable headache on my end [^0], because the Date header was being used for cryptographic signatures. So 1/100 requests would have an invalid signature for no apparent reason. But the reason was Cloudflare not acting as a good proxy, overwriting the Date header that had already been set.
I'd imagine a lot of proxies in general will overwrite that date. At least on the corporate proxy side of things.
`Date` is a registered field [0] used by origin server as defined in RFC 9110 [1]. Any CDN server will add its own date to that header since it's acting as the origin server for that request.
For Cloudflare in particular, you could try setting Cache-Control to Private=Date and see if the edge cache skips the override [2].
What you want seems to be a tunnel with WAF. In that case, a Cloudflare Worker might be a workaround to the native caching layer but I'm not sure if that has any effect on the edge device updating the Date header or not. Workers do support WAF.
0 - https://www.iana.org/assignments/http-fields/http-fields.xht...
1 - https://www.rfc-editor.org/rfc/rfc9110.html
2 - https://developers.cloudflare.com/cache/concepts/cache-contr...
But per RFC 9110 [^0], "the Date header field represents the date and time at which the message was originated." The message comes from my server, not Cloudflare. If they're getting the message from me, i.e. it's not cached by their CDN, they should leave the Date header alone because the message didn't originate with them. [^1]
Maybe I have a misunderstanding of where Cloudflare sits as the "origin server" when their CDN isn't used for caching (i.e. it's bypassed as much as is allowable). I would think my server is the "origin" and theirs is the "edge."
And unfortunately, workers do not allow you to set the Date header -- Cloudflare support and I already tried that a couple years back (i.e. setting Date = Keygen-Date via a worker).
I will take a look at 2. I doubt that'd work, but it's worth a try.
[^0]: https://www.rfc-editor.org/rfc/rfc9110.html#name-date
[^1]: https://httpwg.org/specs/rfc7230.html#rfc.section.5.7.2
But I'm thinking the edge cache is dumb. Some of their docs mention that requests that aren't cached are actually just revalidated and cached at the edge (probably TTL=0) and then served by the dumb edge cache... and they didn't consider they shouldn't be entitled to be the origin in that case.