The answer types for questions in Kinetic Request do not include a type of password. However, this is available as an attribute of the HTML input element - type="password".
To create the password element, you need to put the HTML of the input element in a Kinetic Text Element. Note that the id given to the input element is important and will be needed in the js to save the value to the hidden question.
<p> Password <input type="password" name="pwd" id="123456"> </p>
To make this question appear just like the other question, you'll want to add the standard Kinetic classes for the question label, question answer, and question layer.
<p> <div class="questionLabel">Password</div> <div class="questionAnswer"><input type="password" name="pwd" id="123456"></div> </p>
var answer = document.getElementById('123456').value; KD.utils.Action.setQuestionValue('hidden password question', answer);