diff --git a/src/oauth2server/DatabaseInterface.php b/src/oauth2server/DatabaseInterface.php
index 63ed0980..acf96f97 100644
--- a/src/oauth2server/DatabaseInterface.php
+++ b/src/oauth2server/DatabaseInterface.php
@@ -6,8 +6,8 @@ interface DatabaseInteface
 {
     public function validateClient(
         $clientId,
-        $clientSecret,
-        $redirectUri
+        $clientSecret = null,
+        $redirectUri = null
     );
 
     public function newSession(