Setting If-None-Match Request Headers for Cross-Origin Requests

Question

I need to use the If-None-Match header to stream content to the browser, which I believe is supported by GCS.

I'm getting the signed URL via Firebase Storage, and I've configured my bucket for CORs, but I'm still getting the following in the browser:

Request header field If-None-Match is not allowed by Access-Control-Allow-Headers in preflight response

My CORS configuration for the GCS bucket is:

[
  {
    "origin": ["*"],
    "method": ["GET"],
    "maxAgeSeconds": 3600,
    "responseHeader": ["If-None-Match"]
  }
]

I read that you could include your request headers in response headers field to allow them, but this doesn't seem to work.

What is the best way to achieve this?

Thanks! Leo