s, null) appContexts shall be selected.
 <li>If no provider is selected according to the preceding rules, the factory shall terminate its search for a
 registered provider.
 </ul>
 <p>
 The above precedence rules apply equivalently to registrations created with a null or non-null <code>className</code>
 argument.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>layer</code> - A String identifying the message layer for which the registered AuthConfigProvider is to be returned.
 The v