code: def get_user_metadata(
              self,
              bucket: str,
              key: str
      ) -> typing.Dict[str, str]:
          
          blob_obj = self._get_blob_obj(bucket, key)
          return blob_obj.metadata
docs: Retrieves the user metadata for a given object in a given bucket.  If the platform has any mandatory prefixes or
          suffixes for the metadata keys, they should be stripped before being returned.
          :param bucket: the bucket the object resides in.
          :param key: the key of the object for which metadata is being
          retrieved.
          :return: a dictionary mapping metadata keys to metadata values.