In my opinion it is difficult to figure out what values to put in the variables to download a different jdk version than the default (due to Oracle's site). What do you think of the idea of utilizing alternative binary download locations in addition to the Oracle site. For example, one could utilize the AdoptOpenJDK project's Github published binaries:
https://github.com/AdoptOpenJDK/openjdk11-upstream-binaries/releases
https://adoptopenjdk.net/
Other options include Red Hat or Amazon Corretto.
We could consider the capability to download from any number of sites. I have a couple ideas of how to accomplish this and make it more simple. For example, you could utilize a conditional where if an alternate download file name and url are specified, it utilizes that instead of the Oracle version.