how does something like this pass code and design reviews. is this code written by ai (the buggy code). Not only was the key that signs the cookie inside the cookie it self but it's using pickle which even model weights are moved away from. I'm a little flabbergasted at the noob nature of this root cause.
pickle is nuts, but I can imagine dumping an entire object into the cookie while troubleshooting something then forgetting to clean it up afterwards.
I think you're being unreasonably uncharitable. Any and all software contains bugs, and I can assure you the piece of code you wrote has bugs. My code has bugs. Google's code has bugs. iOS has bugs. rocket launching software has bugs.
We can put in systems in place to catch bugs. And that's the system that's working here.
Now to the second part of the question -
How did they not catch it before? If it were "easy", it would not have been worth 90k, and hindsight is 20/20 - once you know where to look for, it is all very very obvious.