anchor.diff:  -spec start() -> ok | {error, Reason :: term()}.
   start() ->
       {ok, OAI_PMH_PATH} = oz_worker:get_env(oai_pmh_api_prefix),
  -    {ok, LE_CHALLENGE_PATH} = oz_worker:get_env(letsencrypt_challenge_api_prefix),
  -    {ok, LE_CHALLENGE_ROOT} = oz_worker:get_env(letsencrypt_challenge_static_root),
   
       Dispatch = cowboy_router:compile([
           {'_', [
               {OAI_PMH_PATH ++ "/[...]", oai_handler, []},
  -            {LE_CHALLENGE_PATH ++ "/[...]", cowboy_static, {dir, LE_CHALLENGE_ROOT}},
  +            {?LE_CHALLENGE_PATH ++ "/[...]", cowboy_static, {dir, ?LE_CHALLENGE_ROOT}},
               {"/[...]", redirector_handler, https_listener:port()}
           ]}
       ]),
  
positive.code: 
  %% listener_behaviour callbacks
  -export([port/0, start/0, stop/0, healthcheck/0]).
  -export([set_letsencrypt_response/2]).
  
  %%%===================================================================
  %%% listener_behaviour callbacks
  
negative.code: %% for the HTTP authorization challenge.
  %% @end
  %%--------------------------------------------------------------------
  -spec set_response_to_letsencrypt_challenge(Name :: file:name_all(), Content :: binary()) ->
      ok | {error, Reason}
      when Reason :: file:posix() | badarg | terminated | system_limit.
  set_response_to_letsencrypt_challenge(Name, Content) ->
      Path = filename:join(?LE_CHALLENGE_ROOT, Name),
      case filelib:ensure_dir(Path) of
          ok -> file:write_file(Path, Content);
          {error, Reason} -> {error, Reason}
  