[Resolve #1519] Improve error message

sceptre/diffing/stack_differ.py

@@ -197,10 +197,20 @@ def _create_deployed_stack_config(
         try:
             description = stack_actions.describe()
         except ClientError as err:
+            # Check for AWS access exceptions
+            if err.response["Error"]["Code"] == "ForbiddenException":
+                raise SceptreException(
+                    "ForbiddenException: Confirm your current AWS profile is authenticated",
+                    "and has the necessary access.",
+                )
+
             # This means the stack has not been deployed yet
             if err.response["Error"]["Message"].endswith("does not exist"):
                 return None
 
+            # Unknown error, raise it as-is
+            raise err
+
         stacks = description["Stacks"]
         for stack in stacks:
             if stack["StackStatus"] in self.STACK_STATUSES_INDICATING_NOT_DEPLOYED:

tests/test_diffing/test_stack_differ.py

@@ -63,6 +63,7 @@ def setup_method(self, method):
         self._stack = None
         self._actions = None
         self._parameters = None
+        self._describe_fn = self.describe_stack_success
 
     @property
     def parameters_on_stack(self):
@@ -103,6 +104,9 @@ def actions(self) -> Union[StackActions, Mock]:
         return self._actions
 
     def describe_stack(self):
+        return self._describe_fn()
+
+    def describe_stack_success(self):
         return {
             "Stacks": [
                 {
@@ -177,6 +181,17 @@ def expected_deployed_config(self):
             cloudformation_service_role=self.deployed_cloudformation_service_role,
         )
 
+    def test__create_deployed_stack_config__wraps_aws_ForbiddenException(self):
+        def fail_with_ForbiddenException():
+            raise ClientError(
+                {"Error": {"Code": "ForbiddenException", "Message": "No access"}},
+                "describe",
+            )
+
+        self._describe_fn = fail_with_ForbiddenException
+        with pytest.raises(SceptreException):
+            self.differ._create_deployed_stack_config(self.actions)
+
     def test_diff__compares_deployed_template_to_generated_template(self):
         self.differ.diff(self.actions)