image: plumb output proto through to controller

BUG=b:302148521
TEST=run_tests

Change-Id: I1564d5d5871d58f8bc10021fbcfb0ce718b0a928
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4915875
Tested-by: Jack Neus <jackneus@google.com>
Commit-Queue: Jack Neus <jackneus@google.com>
Reviewed-by: Chris Gerber <gerb@google.com>
diff --git a/api/controller/image.py b/api/controller/image.py
index fba8bbd..dee875f 100644
--- a/api/controller/image.py
+++ b/api/controller/image.py
@@ -664,23 +664,25 @@
 @validate.validation_complete
 def SignImage(
     input_proto: "image_pb2.SignImageRequest",
-    _output_proto: "image_pb2.SignImageResponse",
+    output_proto: "image_pb2.SignImageResponse",
     _config: "api.config.ApiConfig",
 ):
     """Sign artifacts based on the given config.
 
     Args:
         input_proto: Input proto.
-        _output_proto: Output proto.
+        output_proto: Output proto.
         config: The API call config.
 
     Returns:
         A controller return code (e.g. controller.RETURN_CODE_SUCCESS).
     """
-    image.SignImage(
+    signed_artifacts = image.SignImage(
         input_proto.signing_configs,
         input_proto.archive_dir,
         Path(input_proto.result_path.path.path),
         input_proto.docker_image,
     )
+    output_proto.signed_artifacts.CopyFrom(signed_artifacts)
+    output_proto.output_archive_dir = input_proto.archive_dir
     return controller.RETURN_CODE_SUCCESS