Sounds like the automaker in question actually did plenty of things right - they put robust auth in place, they didn't roll their own auth / cryptography, they were most of the way there. Yes, security is difficult, but there are some simple rules that you don't need to be a security expert in order to adhere to (I'm definitely not one myself, I'm just a garden variety dev), and that these guys did not follow, in particular:

- Never hard-code credentials (especially in front-end exposed code)

- Never share credentials between environments (especially between prod and non-prod)

And that first rule, in particular, you can (and should) very easily enforce with static analysis tools. If they had just made it harder to shoot themselves in the foot, with basic checks like that, this hack would probably not have been possible.