The solution for what?
If I want the solution for one of my certification projects, I can go to my settings, view the code, and copy-paste it:
Otherwise, if I wanted more, I could automate it by downloading my account info (as you did), and filtering for either:
a) Specific challenge ids to get the solution or files (code)
b) Find all completedChallenges that have either a solution or files field
Hope this clarifies