code: func (f *Form) AddPasswordField(label, value string, fieldWidth int, mask rune, changed func(text string)) *Form {
  	if mask == 0 {
  		mask = '*'
  	}
  	f.items = append(f.items, NewInputField().
  		SetLabel(label).
  		SetText(value).
  		SetFieldWidth(fieldWidth).
  		SetMaskCharacter(mask).
  		SetChangedFunc(changed))
  	return f
  }
docs: // AddPasswordField adds a password field to the form. This is similar to an
  // input field except that the user's input not shown. Instead, a "mask"
  // character is displayed. The password field has a label, an optional initial
  // value, a field width (a value of 0 extends it as far as possible), and an
  // (optional) callback function which is invoked when the input field's text has
  // changed.