Postback dropdowns

What this tests. Category, then subcategory, then results, each step a POST of the whole form with a signed __STATE field you must send back untouched.

The rule. Pick a category and the page posts itself back to list that category's subcategories. Pick a subcategory and it posts again to show the products. Every post must carry the hidden __STATE field exactly as the last page gave it to you; it's signed, so a missing or edited one gets a 400. A subcategory only counts when the state you send back is from a page that already showed its category. Without JavaScript, use the buttons.

• Hard
• HTTP only
• Answer key /forms/postback/answers.json