Fix Azure Arc resource-id UAMI to forward msi_res_id (not mi_res_id)

Live testing against the Azure Connected Machine agent (1.67, user-assigned preview)
showed the Arc token endpoint only honors the IMDS 'msi_res_id' spelling for the
resource-id selector; 'mi_res_id' is silently ignored and returns the system-assigned
identity, so a resource-id UAMI never resolved. Forward 'msi_res_id' on the Arc request
(matching the VM/IMDS source). Update the unit test accordingly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 5ad57850-7d1f-4b9a-bf9f-723d69a9687c

Author: gladjohn

msal/managed_identity.py

@@ -645,7 +645,7 @@ def _obtain_token_on_arc(http_client, endpoint, resource, managed_identity=None)
     if managed_identity:
         _adjust_param(params, managed_identity, types_mapping={
             ManagedIdentity.CLIENT_ID: "client_id",
-            ManagedIdentity.RESOURCE_ID: "mi_res_id",
+            ManagedIdentity.RESOURCE_ID: "msi_res_id",  # Azure Arc honors the IMDS msi_res_id spelling; mi_res_id is ignored and returns the system-assigned identity
             ManagedIdentity.OBJECT_ID: "object_id",
         })
     resp = http_client.get(

tests/test_mi.py

@@ -507,10 +507,10 @@ def test_arc_user_assigned_client_id_should_be_forwarded(self, mocked_stat):
             "client-id",
         )
 
-    def test_arc_user_assigned_resource_id_should_be_forwarded_as_mi_res_id(self, mocked_stat):
+    def test_arc_user_assigned_resource_id_should_be_forwarded_as_msi_res_id(self, mocked_stat):
         self._assert_user_assigned_selector(
             UserAssignedManagedIdentity(resource_id="resource-id"),
-            "mi_res_id",
+            "msi_res_id",
             "resource-id",
         )