@ypid good catch.
We have a plugin-test command that ensures plugins work properly and meet our standards. Can you think of a way to automatically check for HTTP downloads in our plugin-test command? I suppose we stub curl and wget and see what arguments they are passed. If it's not automated it's probably not going to happen...
The easiest and most effective step would be to check all source code of plugins and enforce that no unauthenticated legacy HTTP connection attempts are to be made. Ref: https://github.com/asdf-vm/asdf-nodejs/pull/16
And maybe a warning could be given if no gpg command is used which is commonly used to verify signatures.
I will close this issue, as it has been inactive for a long time now.
If there is still interest, please feel free to open a new issue.
Thank you!