It's fairly standard for network clients to assume potential malicious control of the server they are connecting to.

It helps reduce the blast radius of a compromised server.

In the case where the server is operated by a third party (as is the case with the B2 API server), there can be many compliance implications if that third-party-operated server has access to an internal network.

We don't accept when SSH clients or web browsers have the ability to do things they shouldn't based on instructions sent by the server they connect to.

Why would we suddenly have lower expectations of our file storage API clients? (or any other network/HTTP clients for that matter)