This program makes heavy use of https://github.com/thorsten-gehrig/alexa-remote-control, found here under ~/github, with some minor modifications.
alexa-remote-control requires sudo install jq for command-line parsing of JSON output.
Getting and saving required cookies was the hardest part. Lots of good advice at https://www.codementor.io/@slavko/controlling-amazon-echo-dot-with-shell-a-bit-of-fun-mz6xxz92n.
Note that in order to get the cookies required by the above onto my RPi, I had to:
sudo apt install vnc4server
sudo apt install lxsession
sudo apt install firefox-esr
After installation of the above, I needed to do a sudo raspi-config to enable VNC through the Interfaces menu item.
I also needed to sudo apt install realvnc-vnc-viewer onto my Ubuntu laptop, as remmina did not work.
Logged in to the Pi desktop via vncviewer 192.168.1.6 from the laptop ('pi'/'B3st')
Once I got to a desktop on the Pi, I started Firefox and installed the Export Cookies add-on, after which I went to https:\\alexa.amazon.com and exported cookies in the amazon.com domain (clear all cookies first). This file was eventually saved to the ~/.alexa-remote-control/.alexa.cookies file for Capcha-free logins through cURL and wget.
The format of the creds.json file for authenticating to the Tesla gateway is:
{"username":"customer","password":"my_password", "email":"my_email","force_sm_off":false}
Note that "username" above is literally "customer" (as opposed to "installer")