anchor.diff:  get_user(UserSubject, Issuer) ->
       load_or_return_user(#{ sub => UserSubject, iss => Issuer}).
   
  --spec user_shutting_down(ID :: binary()) -> ok.
  -user_shutting_down(ID) ->
  -    gen_server:call(?MODULE,{delete_user,ID}).
  +-spec user_wants_to_shutdown(ID :: binary()) -> ok.
  +user_wants_to_shutdown(ID) ->
  +    gen_server:call(?MODULE,{user_wants_to_shutdown,ID}).
   
   %% gen_server.
   
  
positive.code:     case add_new_user_entry(UserId,Pid) of
          ok -> 
              {ok, Pid};
          _ ->
              ok = tts_user:stop(Pid),
              lookup_user(UserMap)
      end.
  
negative.code: %% API.
  -export([start_link/0]).
  -export([get_user/2]).
  -export([user_wants_to_shutdown/1]).
  
  %% gen_server.
  -export([init/1]).
  