SEC-1073: Correct class name in docbook namespace chapter.

src/docbkx/namespace-config.xml

@@ -763,7 +763,7 @@
     <para>
       We've touched on the idea that the namespace configuration automatically registers an authentication manager bean for
       you. This is an instance of Spring Security's <classname>ProviderManager</classname> class, which you may already 
-      be familiar with if you've used the framework before. You can't use a custom <classname>AuthenticationProvider</classname> if you are
+      be familiar with if you've used the framework before. You can't use a custom <classname>AuthenticationManager</classname> if you are
       using either HTTP or method security through the namespace, but this should not be a problem as you have full control over 
       the <classname>AuthenticationProvider</classname>s that are used.
     </para>