Pin code as protection code

Hello.

When we check balance we place code of gift card like 3DGY-6F57-7N6G-8VSL.

When we want to add more funds to it we have to use link like

?pw_gift_card_reload_number=3DGY-6F57-7N6G-8VSL

1. So, any search engine can cache this string ;
2. If I want to send this string to my friends this code can be redeemed.
3. etc.

So how can we add Pin code?(protection code) to redeem each code, to use it more secure ?

So users can use only code to Fund, see balance. But to redeem there should be additional protection.