Firefly Services InDesign API - Input/ output assets domains question

Looking through the docs and some example code in github for the InDesing APIs through Firefly services I can see that the input/output assets list AWS S3, Dropbox, and Azure as the supported assets. However it looks like these are just utilizing signed/ pre-signed URLs, and they are not the only cloud services which support this style of access to assets.

Is it possible to use a different cloud storage system for assets with Firefly InDesign APIs assuming it can generate a signed url for use by the Adobe backends? Specifically I want to know if it is possible to utilize these APIs with signed URLs for Google Cloud Storage assets.

From the reading the docs, I strongly doubt this would work as is, since there's likely a domain based whitelist for these assets. But I'm especially curious if it's feasible to get a domain whitelisted.

Context
I'm working on a design for automating some manual steps in a workflow where we convert INDD to IDML. I'm considering either Firefly Services InDesign API or InDesign Server. But neither fits the requirements exactly. Specifically: I may have a hard requirement for assets to be stored in Google Cloud Storage, and there's a very strong preference for not self-hosting a Windows machine to handle this conversion.

This may not be the correct channel to pose this question, if there's a better avenue let me know.