Add early acceptance test for reauthentication.
diff --git a/authenticate.go b/authenticate.go
index 8b87e44..7665304 100644
--- a/authenticate.go
+++ b/authenticate.go
@@ -139,3 +139,8 @@
 func (a *Access) AuthToken() string {
 	return a.Token.Id
 }
+
+// See AccessProvider interface definition for details.
+func (a *Access) Revoke(tok string) error {
+	return nil
+}