Since relatively few commerical hosting sites provide JSP or Servlet support (as compared with PHP support), this may not be a mainstream solution---but since I teach a Java Servlet based web development course, I already have a running Tomcat installation, so it was a good fit for me.

It can be configured to use a MySQL database for username/passwords, but the default install doesn't require it---it implements its own user database, storing the data in an XML file.