Hello! I don’t have any examples of your exact use case, but a few things for you to review that I think will help you figure out the workflow.
The first is we have a Velo package (similar to an npm package but specifically for velo if you haven’t seen these yet) for HMAC authentication to protect your http functions.
The second is a tutorial created by a Velo user on using firestore with Wix/Velo that will cover concepts that can apply to your use case
Take a look at these and let me know you thoughts or other questions