diff --git a/src/emqx_types.erl b/src/emqx_types.erl
index 2fe34e853..586a1aef0 100644
--- a/src/emqx_types.erl
+++ b/src/emqx_types.erl
@@ -40,10 +40,19 @@
 -type(username() :: maybe(binary())).
 -type(password() :: maybe(binary())).
 -type(peername() :: {inet:ip_address(), inet:port_number()}).
+-type(auth_result() :: success
+                     | client_identifier_not_valid
+                     | bad_username_or_password
+                     | not_authorized
+                     | server_unavailable
+                     | server_busy
+                     | banned
+                     | bad_authentication_method).
 -type(protocol() :: mqtt | 'mqtt-sn' | coap | stomp | none | atom()).
 -type(credentials() :: #{client_id := client_id(),
                          username  := username(),
                          peername  := peername(),
+                         result    := auth_result(),
                          zone      => zone(),
                          atom()    => term()
                         }).