Web service login help

I need help with setting up a web service (using JBOSS along with MySQL) call that allows users to login/register. Also, how do you validate the parameters received from a web service routine, e.g. do u have use JAXB to validate against the XML schema or if there is simpler way to do that ?
My web service call is and its a top down web service application.
public void VerifyUser(String username, String userPassword)
{

}