download.file fails due to outdated certificates

Hello,
I ask my students to use rstudio.cloud when they cannot install rstudio directly (because e.g. they only have a chromebook or a tablet).

As downloading R scripts is generally a nightmare, especially for newbies, I adopted the following routine, which works for everyone regardless of their OS, browser, and use of posit.cloud:

  • all course lectures are distributed as html files on my universty home page
  • each course starts with a download.file command to download the corresponding R file

This has been foolproof for years, and worked for students using their own computer, PCs in the computer room, or posit.cloud (without the hassle of having to upload the scripts for the latter).
Until my university started using a new certificate for their servers.
Since then, all the downlad.file commands fail. I have the same issue on older Linux installations. My question is, how do I ask posit staff to upgrade their certificates? I am guessing the issue is with the ca-certificate package. BTW I already tried switching to Ubuntu 24 but it does not make a difference.
Thanks a lot for your attention.