When the textbox type is wanted to set in a richlet, it have to be hard-coded, or the type have to be defined in a custom constant. For instance:

Textbox textbox = new Textbox();
textbox.setType("password");
...

It would be great the type constants is provided by ZK framework. So the type can be set like:

Textbox textbox = new Textbox();
textbox.setType(Textbox.TEXT);
...

I've attached a patch which can help you to implement that feature.