Confirm Password with jQuery Validate

I'm trying to use jQuery validate plugin to confirm my password entry.

However, I don't want it to be a required field.

Just IF a user wants to change the password, they would need to confirm it.

If not, both fields shouldn't be validated.

jQuery('.validatedForm').validate({
    rules: {
        password: {
            required: true,
            minlength: 5
        },
        password_confirm: {
            required: true,
            minlength: 5,
            equalTo: "#password"
        }
    }
}); 

This is working perfectly, but again, both fields are required.

I would like to have this optional, in case someone just wants to change for instance their email or username and leave the password alone.