Adds user-facing error message for login path.
Adds user-facing error message for login path.

martijnengler/mycli,j-bennet/mycli,mdsrosa/mycli,mdsrosa/mycli,jinstrive/mycli,danieljwest/mycli,martijnengler/mycli,danieljwest/mycli,jinstrive/mycli,j-bennet/mycli