### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

--- Short Version: --- Confirming this issue with reproducible data.

- LiteLLM `1.83.14`, `chatgpt/*` OAuth device flow - Requests to `https://chatgpt.com/backend-api/codex/chat/completions` return Cloudflare challenge HTML / 403 - Reproduced from two different hosts with same egress IP (so not a single-host routing issue)

Key debug finding: - LiteLLM outbound request includes Authorization + User-Agent - **No Cookie header present** - Challenge HTML is returned instead of JSON

So valid OAuth token alone is not sufficient in this environment for this endpoint path. This appears to be a ChatGPT-provider compatibility gap in LiteLLM under Cloudflare challenge conditions.

--- Longer Version: --- We can reproduce this consistently in a dual-host setup and can confirm it is not just a single-host network anomaly.

## Environment - LiteLLM: `1.83.14` - Provider path: `chatgpt/*` (ChatGPT subscription OAuth device flow)

## Reproduction summary 1. OAuth auth file is present and valid (`access_token`, `refresh_token`, `id_token`, non-expired `expi…