> By the go module cache system design, if you trust the server set in your GOSUMDB env var,
> which is defaulted to
sum.golang.org, then it is not a matter whatever proxy server your are using.
From the point of view of downloaded package integrity, yes.
But there are other things an untrustworthy proxy might do - such as tracking what packages and versions you use, identifying which clients are using packages with known security vulnerabilities, selling that data on to third parties etc.