s called, the following processing
    is required:</p>
    <ul>
    <li>Acquire the one and only connection [Current] or acquire a connection
        from the connection pool [Requested].</li>
    <li>Authenticate the user by retrieving the user's Distinguished Name,
        based on the specified username and password.</li>
    <li>If the user was not authenticated, release the allocated connection
        and return <code>null</code>.</li>
    <li>Acquire a <code>List</code> of the security roles assigne