diff --git a/modules/gatewayInterface.py b/modules/gatewayInterface.py
index 92e0c91f..e499245c 100644
--- a/modules/gatewayInterface.py
+++ b/modules/gatewayInterface.py
@@ -356,14 +356,14 @@ class GatewayInterface:
         user = next((u for u in users if u.get("username") == username), None)
         
         if not user:
-            return None
+            raise ValueError("Benutzer nicht gefunden")
         
         if not self._verifyPassword(password, user.get("hashedPassword", "")):
-            return None
+            raise ValueError("Falsches Passwort")
         
         # Check if the user is disabled
         if user.get("disabled", False):
-            return None
+            raise ValueError("Benutzer ist deaktiviert")
         
         # Create a copy without password hash
         authenticatedUser = {**user}