anchor.diff:  get_user_info(Issuer, Subject) ->
       retrieve_userinfo_if_exists(Issuer, Subject).
   
  +-spec verify_cache() -> ok.
  +verify_cache() ->
  +    gen_server:cast(?MODULE,verify_cache_validity).
   
   %% gen_server.
   %% TODO: implement a cleaning preferably in tts_data or similar
  
positive.code: %% API.
  -export([start_link/0]).
  -export([get_user_info/2]).
  
  %% gen_server.
  -export([init/1]).
  
negative.code: handle_call(_Request, _From, State) ->
  	{reply, ignored, State}.
  
  handle_cast(verify_cache_validity, State) ->
      Interval = ?CONFIG(cache_check_interval),
      timer:apply_after(Interval,?MODULE,verify_cache,[]),
      verify_cache_validity(),
  	{noreply, State};
  handle_cast(_Msg, State) ->
  	{noreply, State}.
  
  handle_info(timeout, State) ->
      Interval = ?CONFIG(cache_check_interval),
      case Interval of 
          undefined ->
              {noreply,State,5000};
          _ ->
              timer:apply_after(Interval,?MODULE,verify_cache,[]),
              {noreply,State}
      end;
  handle_info(_Info, State) ->
  