This is an easily solved problem. Backblaze has an example here: https://github.com/backblaze-b2-samples/cloudflare-b2
This looks like an awful lot of setup for "easily solved". Easily solved is what S3 does where this isn't even a problem.
curl -sL https://github.com/backblaze-b2-samples/cloudflare-b2/raw/main/README.md | head -n 1
# Cloudflare Worker for Backblaze B2
yes, it's a worker