How do I stop KWallet from asking my password to let the system connect to WiFi?

On KDE 5, in the System Settings app KDE Wallet, enable the option Different wallet for local passwords.

Then: create a new wallet for this option, select Blowfish encryption for it, and click OK to set a BLANK password.

WiFi passwords now get chucked into this wallet and there's no password prompt to "open" it whenever the system needs access to it.

(Note: KWallet is both annoying as well as insecure, as it allows any app to request full access to all passwords stored in a wallet once that wallet is open...)

There will by only lack of encryption on password file.

If you encrypt whole your system, then there is no problem :)

The problem is that KDEWallet will manage all encrypted passwords unless disabled (bad idea in my opinion), so in order to avoid having to put the password for wifi, you will have to avoid encryption on wifi networks.

All you have to do is go to "Networks"(Wifi Icon) then "Configure Network Connections" (Looks like sliders) then choose on the left panel the wifi you want to configure then on the right side of the menu choose the TAB "Wifi security" finally you will see below "Store password for this user only (encrypted)" change it to "store password for all users (not encrypted)"

You just have to remember this when adding more networks.