Lowercase instance name follows Token Cache schema

Author: rayluo

msal/managed_identity.py

@@ -254,7 +254,7 @@ def __init__(
 
     def _get_instance(self):
         if self.__instance is None:
-            self.__instance = socket.getfqdn()  # Moved from class definition to here
+            self.__instance = socket.getfqdn().lower()  # Moved from class definition to here
         return self.__instance
 
     def acquire_token_for_client(