Simply relying on package signing and the like permits trusted but malicious actors. With Deno packages configured well it can really lock down and limit a ton of attack vectors.
I...think you might have bigger problems going on there. You're tryingto throw a tech solution at a problem that is fundamentally human in nature.
That tends to leave nobody satisfied.
Unfortunately, package signing does nothing to protect against the threat vector presented here. The authentication system in npm is working fine. The problem is we put too much trust in software from the internet.
Alice has a thing. Bob had a thing that Alice figured would make her life easier so integrates it without looking too hard at it. Alice didn't reallize that by adding Bob's thing, something Alice wanted private was no longer the case even if her primary use case was solved.
The technical solution is making Alice's thing include a really onerous to configure permissions framework that takes the work of getting a thing set up and increases the task list from program thing to program and configure permissions for thing.
The human solution is to realize you don't know Bob from Adam, or his motivations, and to observe what Bob's thing actually does. Then depending on criticality, remake something similar, or actually take the time to get to know Bob and see if he can make what you want for you under some sort of agreement that facilitates good business and trust all around. You can't be sampling for malicious changes in real-time, so it's all about risk management. The issue in our case, is a lot of these projects are essentially gifts with no active attention paid to them after a certain point. It's a variant of cargo cults. You want this thing? Go here, get that, presto. Businesses, developers, (and their exploiters) like that. The price though is that once a project is abandoned, and the rights transferred to someone you don't know, you have to rerun your risk management calculation again.
The thing people should be worried about is all the PHB's (pointy-haired bosses) who just got ammo for their NMIH (Not-Made-In-House) cannons now that supply chain attacks are becoming increasingly visible vectors for attack.
