How can I add metadata to every call?

[howdymatt]

I have a use case where I need to pass along metadata with each LLM request, since I use a proxy to log and report on all LLM usage. Similar to LiteLLM/Langfuse integration, as sample call would look like:

{
    "model": "gpt-3.5-turbo",
    "messages": [
        {
        "role": "user",
        "content": "what llm are you"
        }
    ],
    "metadata": {
        "trace_id": "trace-id22",
        "trace_user_id": "user-id2"
    }
    ```
    
    Is there a way to capture the call and add the metadata before sending?