 <code>getRemoteUser</code>, and <code>getAuthType</code> return null), and when validation of the provided
 credentials is successful. Otherwise, this method throws a <code>ServletException</code> as described below.

 <p>
 When this method returns without throwing an exception, it must have established non-null values as the values
 returned by <code>getUserPrincipal</code>, <code>getRemoteUser</code>, and <code>getAuthType</code>.</div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>username</code> - 