When the popover view opens, my extension try to read credentials of the keychain.
Then a keychain window opens and ask for a password. Impossible to type into the password field a password. The entered keys are ignored.
This is a serious bug in mac os. I sent this even to feedback assistant, but got no response.
Feedback ID: FB7665923
As workaround, you can copy the password into the clipboard and then doing right mouse click to paste it.
