The following code will show you how to deactivate auto fill for a HTML form. I think that is what you need. But I do not know how to set this value in Java. autocomplete="off"
is the magic parameter.
<form action="demo_form.asp" method="get" autocomplete="off">
First name:<input type="text" name="fname"><br>
E-mail: <input type="email" name="email"><br>
<input type="submit">
</form>
Edit: I found something at https://issues.apache.org/jira/browse/WICKET-1504, but I'm not sure if it works.
newPassword.put("autocomplete", "off");
and the same for the username input field object.