Someone thought they were improving password security by discouraging the use of the clipboard.
A relatively simple work around is to use a program such as AutoHotKey to "paste" from the clipboard:
https://autohotkey.com
On Windows, I use the following script that uses Ctrl-Alt-v to "paste" from the clipboard into text fields that block Ctrl-v:
^!v:: ; paste without formatting
plainpaste:
StringReplace, clipboardt, clipboard, `r`n, %A_Space%, All
clipboardt := RegExReplace(clipboardt, "` {2,}", "` ")
StringLeft, 1st, clipboardt, 1
IfInString, 1st, %A_Space%
StringTrimLeft, clipboardt, clipboardt, 1
Send %clipboardt%
clipboardt =
return