diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index 14ebd7fa5..47211ade1 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -120,6 +120,10 @@ configuration file.
 Authentication Plugins
 ----------------------
 
+.. NOTE::
+
+    This feature is only supported by Keystone for the Identity API v3 clients.
+
 Keystone supports authentication plugins and they are specified
 in the ``[auth]`` section of the configuration file. However, an
 authentication plugin may also have its own section in the configuration