Digital Ocean App Platform Stripping If-Modified-Since Header

I am implementing my own caching for certain endpoints on my server around If-Modified-Since and the header is getting stripped out before making it to my app. I know the app platform is behind Cloudflare so this isn’t super surprising but I can’t find this behavior documented anywhere.

Here I am making my request:

const headers = new Headers();
if (lastUpdatedRef.current) {
  headers.append("if-modified-since", lastUpdatedRef.current);
}

const resp = await fetch("/api/vehicle-positions", { headers });
if (resp.status === 304) {
  return; // No new data
}

And on the server when I log all of the headers it is not there:

const ifModifiedSince = req.headers.get("if-modified-since");
const clientDate = ifModifiedSince && new Date(ifModifiedSince);
console.log(req.headers); // headers without any if-modified-since
console.log("dates", currentUpdatedAt?.toUTCString(), clientDate); // dates Sun, 04 May 2025 16:52:37 GMT null

Is there any way I can get this header or should I just send it as a custom header?