How to make litellm proxy return the headers from llm provider?

[lyajedi]

according to https://docs.litellm.ai/docs/proxy/response_headers#response-headers-from-llm-providers

LiteLLM also returns the original response headers from the LLM provider. These headers are prefixed with llm_provider- to distinguish them from LiteLLM's headers.

However, I never see any llm_provider- prefix headers in response, the provider returns lots of additional headers like with x- in it, but they are all removed in the proxy response.