anchor.diff:  -export([code_change/3]).
   
   -record(state, {
  +          sub = undefined,
  +          iss = undefined,
             user_info = #{},
             credentials = [],
             sessions = []
  
positive.code: -include("tts.hrl").
  
  %% API.
  -export([start_link/0]).
  -export([set_user_info/2]).
  -export([get_user_info/1]).
  -export([get_credential_list/1]).
  
negative.code: 
  %% API.
  
  -spec start_link(Subject::binary(), Issuer::binary()) -> {ok, pid()}.
  start_link(Subject, Issuer) ->
  	gen_server:start_link(?MODULE, [Subject, Issuer], []).
  
  -spec set_user_info(UserInfo :: map(), Pid :: pid()) -> ok.
  set_user_info(Info, Pid) ->
  