You said "Front load my interactive input:" and also "Request a token, before gcloud is even installed". The problem with your request above, is that you will need to install gcloud at some point in time and gcloud will use its own authentication methods to connect, meaning that authentication should happen after gcloud is installed because you will always use the command “gcloud ….” to somehow connect. The previous post that you linked explains this.
Due to this, I'm suspecting that you need a workflow where simultaneous gcloud commands will run on multiple users/projects at the same time, by running gcloud many times in parallel. As you know, Linux runs one command at a time and "front loading" the authentication (as you call it) can either be the "screen" command inside one SSH session or running multiple SSH sessions at the same time. If that's not what you need, then a simple shell script should do. The shell script will run commands one after the other rather than in parallel.
For example, let's say that you want to install a package that will take a long time and be able to run another command at the same time, then you could do the following:
$ screen
$ sudo apt-get install [package-name]
Press Ctrl-A” and “d“ to temporarily exit this session
$ … (do another process here)
$ screen -r (re-attaches screen to continue on previous process on line 2)
The example above is somewhat the equivalent of having multiple SSH sessions open at the same time. You could maybe open multiple “screens” and launch multiple authentications at the same time, thereby also controlling when you want to stop a session. Keep in mind that if you run things in parallel, you will definitely need to load the authentication file as mentioned in the post you linked. Otherwise, you can use simple shell scripting and pass arguments. Since i'm not sure of the process that comes before/after your authentication, it's hard for me to provide a more precise example. There's a lot to consider and many unknowns about your workflow. I've included references below that show all the possibilities.
References:
- https://www.linode.com/docs/networking/ssh/using-gnu-screen-to-manage-persistent-terminal-sessions/
- https://www.geeksforgeeks.org/screen-command-in-linux-with-examples/
- https://www.lifewire.com/pass-arguments-to-bash-script-2200571
- https://cloud.google.com/sdk/gcloud/reference/auth/activate-service-account
- https://cloud.google.com/sdk/gcloud/reference/auth/login
- https://cloud.google.com/sdk/docs/scripting-gcloud