diff --git a/dudeswave/src/dudeswave_auth.erl b/dudeswave/src/dudeswave_auth.erl
index 815292b..4c850d9 100644
--- a/dudeswave/src/dudeswave_auth.erl
+++ b/dudeswave/src/dudeswave_auth.erl
@@ -74,12 +74,14 @@ Authenticate a user and return a new cookie for the new session.
 Spec:
 
 ```
--spec authenticate(User, Password, Cookies, Bucket) -> {true, Cookie} | false | {error, Reason} when
+-spec authenticate(User, Password, Cookies, Bucket) -> {true, Cookie, Validity} |
+    false | {error, Reason} when
 	User :: binary(),
 	Password :: binary(),
 	Cookies :: atom(),
 	Bucket :: atom(),
 	Cookie :: binary(),
+	Validity :: non_neg_integer(),
 	Reason :: term().
 ```