That's an interesting idea actually. My first response was that you can't freely interact with the clipboard but you can set it provided you do it in response t

That's an interesting idea actually. My first response was that you can't freely interact with the clipboard but you can set it provided you do it in response to a js event so in theory that is possible. The only problem is that you'd need to be sure the clipboard did actually contain the password because of course you can't read it. I guess you can log whether onpaste fired and then if the login button is clicked with a second or two, clear the clipboard.