CIMD Fetch Failed with 403 from Cloudflare worker

I’ve got an MCP server hosted in Cloudflare that only supports CIMD and not DCR. It works fine in Claude. Trying to connect to it from ChatGPT, we get a 403 when reaching out to the CIMD client metadata URL. I can reach it fine locally, so it seems like it might be some kind of WAF or bot prevention blocking my Cloudflare worker from reaching it. This is the message I get in my logs when it fails:

“CIMD fetch failed for https ://chatgpt.com/oauth/snip/client.json:”

“Failed to fetch client metadata: HTTP 403”

I’ve figured out how to easily reproduce this by sending a Cloudflare header: “Cf-Worker: whatever” makes it 403