diff --git a/README.txt b/README.txt
index e614c37..6ffe54b 100644
--- a/README.txt
+++ b/README.txt
@@ -29,3 +29,8 @@ A2_LTPA_COOKIE_DOMAIN
 A2_LTPA_COOKIE_HTTP_ONLY
 
     Should the cookie be only sent with HTTP request, default is true.
+
+A2_LTPA_ADAPTER
+
+    Class to adapt username for the LTPA idp, default is
+    'authentic2_idp_ltpa.adapter.UserAdapter'