Broaden prototype scope?

Maybe here or in a separate repo. Feedback from jas on sigsum-general:

• Not github specific prototype would be nice, jas is interested in
  • GitLab release pages
  • Savannah download area
  • ftp.gnu.org
• Download artifacts from >1 project
• Download signatures from >1 sigsum key

And some point it was also mentioned "just use files from disk" instead of downloading? And then I pointed to https://git.glasklar.is/rgdd/sshdt which basically does that for the sigsum+ssh prototype that logs commands before execution.