GUACAMOLE-96: Add redecorate() function with semantics analogous to updateUserContext().

extensions/guacamole-auth-header/src/main/java/org/apache/guacamole/auth/header/HTTPHeaderAuthenticationProvider.java

@@ -114,6 +114,13 @@ public class HTTPHeaderAuthenticationProvider implements AuthenticationProvider
         return context;
     }
 
+    @Override
+    public UserContext redecorate(UserContext decorated, UserContext context,
+            AuthenticatedUser authenticatedUser, Credentials credentials)
+            throws GuacamoleException {
+        return context;
+    }
+
     @Override
     public void shutdown() {
         // Do nothing