Hence you need to start thinking about threat models and levels of compromise, even in your build system.

If I control the issuing and governance of these short-lived secrets, they very much help against many attacks. Go ahead and extract an upload token for one project which lives for 60 seconds, be my guest. Once I lose control how these tokens are created, most of these advantages go away - you can just create a token every minute, for any project this infrastructure might be responsible for.

If I maintain control about my pipeline definition, I can again do a lot of work to limit damage. For example, if I am in control, I can make sure the stages running untrusted codes have as little access to secrets as possible, and possibly isolate them in bubblewrap, VMs, ..., minimize the code with access to publishing rights. Once I lose control about the pipeline structure, all that goes away. Just add a build step to push all information and secrets to mastodon in individual toots, yey.

To me, this has very much raised questions about keeping pipeline definitions and code in one repository. Or at least, to keep a publishing/release process in there. I don't have a simple solution there, especially for OSS software with little infrastructure - it's not an easy topic. But with these supply chain attacks coming hot and fast every 2 weeks, it's something to think about.