 and return <code>null</code>.</li>
    <li>Acquire a <code>List</code> of the security roles assigned to the
        authenticated user.</li>
    <li>Construct a new instance of class
        <code>org.apache.catalina.realm.GenericPrincipal</code>, passing as
        constructor arguments:  this realm instance, the authenticated
        username, and a <code>List</code> of the security roles associated
        with this user.</li>
    <li><strong>WARNING</strong> - Do not attempt to cache and reuse previou