anchor.diff:  %% but may not contain all required fields.
   %% @end
   %%--------------------------------------------------------------------
  --spec prepare_helper_args(name(), #{binary() := binary()}) -> args().
  +-spec prepare_helper_args(name(), args()) -> args().
   prepare_helper_args(HelperName = ?S3_HELPER_NAME, Params) ->
       Transformed = maps_flatmap(fun
           (<<"hostname">>, URL) ->
  
positive.code:     filter_params(expected_helper_args(HelperName), Params).
  
  
  prepare_user_ctx_params(HelperName, Params) ->
      filter_params(expected_user_ctx_params(HelperName), Params).
  
  
negative.code: 
  
  % @fixme support creating webdav ctx with adminId
  
  % @fixme move ctx managemetn to other module
  
  %%%===================================================================
  %%% API
  