add to wn

Author: rustagir

source/whats-new.txt

@@ -47,9 +47,7 @@ What's New in 1.13
 
 - Added a custom authentication provider interface for Source and Sink
   Connectors. This feature enables you to write and use a custom implementation
-  class in your connector.
-
-.. TODO add link To learn more, see the :ref:`` guide.
+  class in your connector. To learn more, see the :ref:`kafka-custom-auth` guide.
 
 - Fixed an issue that occurred when validating configuration for Source
   and Sink Connectors if the configuration contained secrets and used