When I run apt update, apt reaches out to its repositories and downloads index files. How can I see the exact URL for every downloaded file?

Here's an example:

apt update

Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease

Hit:2 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease

Hit:3 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease

Hit:4 http://security.ubuntu.com/ubuntu bionic-security InRelease

Hit:5 https://artifacts.elastic.co/packages/8.x/apt stable InRelease

Reading package lists... Done

Building dependency tree

Reading state information... Done

108 packages can be upgraded. Run 'apt list --upgradable' to see them.

Those apt update response lines look like URLs, but they're translated behind the scenes into something else. What is that "something else"? I'm looking for the full, precise URL of every file that apt is downloading with this command.

A little background: I'm trying to proxy the artifacts.elastic.co packages. I can't find the right path to use. The artifacts.elastic.co refuses to show the contents of directories, so I'm unable to use a web browser to look around for the correct magic path/URL.

Note: even though my example uses, apt, using apt-get or any other tool which shows me the full URL would be an acceptable answer.