[s3] Pass object parameters to head_object in exists

When using server-side-encryption with customer-provided keys (SSE-C),
the head_object call needs the SSE-C key and algorithm - otherwise the
call will fail with `botocore.exceptions.ClientError: An error occurred (400)
when calling the HeadObject operation: Bad Request` if the file already
exists.

storages/backends/s3.py

@@ -583,8 +583,9 @@ def exists(self, name):
             return False
 
         name = self._normalize_name(clean_name(name))
+        params = _filter_download_params(self.get_object_parameters(name))
         try:
-            self.connection.meta.client.head_object(Bucket=self.bucket_name, Key=name)
+            self.connection.meta.client.head_object(Bucket=self.bucket_name, Key=name, **params)
             return True
         except ClientError as err:
             if err.response["ResponseMetadata"]["HTTPStatusCode"] == 404:

tests/test_s3.py

@@ -503,6 +503,18 @@ def test_storage_exists(self):
             Key="file.txt",
         )
 
+    def test_storage_exists_ssec(self):
+        params = {"SSECustomerKey": "xyz", "CacheControl": "never"}
+        self.storage.get_object_parameters = lambda name: params
+
+        self.storage.file_overwrite = False
+        self.assertTrue(self.storage.exists("file.txt"))
+        self.storage.connection.meta.client.head_object.assert_called_with(
+            Bucket=self.storage.bucket_name,
+            Key="file.txt",
+            SSECustomerKey="xyz"
+        )
+
     def test_storage_exists_false(self):
         self.storage.file_overwrite = False
         self.storage.connection.meta.client.head_object.side_effect = ClientError(