Nothing on openHAB is secure. Even the REST endpoints and transmission are sent in the clear. What you are trying to do is basically mimicking security and just adding one more step before something occurs.
I already have the keypad widget for HABPanel. What you can do is setup a rule to a proxy item. If that proxy item changes, then the receivingItem for the keypad must match. Again, this is not ‘security’ but more of safety.
This seems to be an interesting feature. I’ll see what I can come up with..