WiFi connection management in Ubuntu as option to Show Password. If PC unlocked then someone can check what is the password set for WiFi. Ideally there should not be Show Password option at all. If this is required then Ubuntu should first invoke the person to enter PC password to edit the WiFi password.
I think you may have answered your own question.
If you are at the lock screen, you cannot access the WIFI settings.
This means that an authorized user must be logged in before you can get to those settings.
Now, the problem sounds to me like you are worried about a security hole that all network admins no matter what platform have to worry about:
Users walking away and leaving their PCs unlocked.
The best answer here is to enforce a policy of users being reprimanded for not locking their PC when they leave their seats.
Just FYI, our Windows friends have the same issues.
This article also covers PCs as well as older versions of Windows.
Then what you are really looking for is to request a feature, here is the best place to do that:
Based on reading this thread:
Because as of now this is not a feature in any OS as far as I know, so you will need to start by requesting it as one first.