Gmail API authentication redirect not working on AWS EC2

Question

I'm trying to run a python script that interacts with the GMail Api on AWS EC2. Said script SHOULD either process the authenticated inbox or ask for authentication if the token doesn't exist. This authentication normally takes the form of opening up a browser window. This works on localhost but doesn't work on my EC2 instance.

I've tried running a webserver using Flask (accessible through its public IP) and having the call to the script be the result of clicking a button. When I do this, I get other interactivity from the Flask script and the authentication URL prints out on the CLI, but I'm not redirected.

I've tried just running the script from the CLI, but that obviously doesn't work. That last one might've just been desperation and/or wishful thinking.

EDIT: Info - The URL seems auto-generated so I don't know it ahead of time.