revise to make auth provider more general

Author: rustagir

source/whats-new.txt

@@ -45,8 +45,9 @@ Learn what's new by version:
 What's New in 1.13
 ------------------
 
-- Added a custom authentication provider interface to support AWS IAM
-  authentication for Source and Sink Connectors.
+- 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.