Proxy video from Google Cloud Storage

I'm using the REST API for GCP Cloud Storage to fetch JSON documents without any problems, but when I'm trying a .webm or .mp4 video, I keep getting only the JSON metadata (same you get if you don't add the "?alt=media" querystring to the Cloud Storage call. The strange thing is, I can easily proxy .webm videos from other sites. It's almost if Cloudflare Workers is rewriting the HTTP headers in the sub requests. Anyone know anything about this?
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