anchor.diff:  		LastModified :: {integer(), integer()},
   		Reason :: term().
   %% @equiv add_user(Username, Password, UserData, Address, Port, Dir)
  -add_user(Username, Password, UserData) ->
  +add_user(Username, Password, UserData)
  +			when is_list(Username), is_list(Password) ->
   	try
   		{Port, Address, Dir, _} = get_params(),
   		add_user(Username, Password, UserData, Address, Port, Dir)
  
positive.code: 		LastModified :: {integer(), integer()},
  		Reason :: term().
  %% @equiv add_user(Username, Password, UserData, Address, Port, Dir)
  add_user(Username, Password, UserData, Port, Dir) ->
  	try
  		{_, Address, _, _} = get_params(),
  		add_user(Username, Password, UserData, Address, Port, Dir)
  
negative.code: 		Reason :: term().
  %% @equiv mod_auth:add_user(Username, Password, UserData, Address,
  %% Port, Dir)
  add_user(Username, Password, UserData, Address, Port, Dir)
  			when is_list(Username), is_list(Password),
           is_list(UserData), is_integer(Port), is_list(Dir) ->
  	LastModified = {erlang:system_time(?MILLISECOND),
  			erlang:unique_integer([positive])},
  	NewUserData = [{last_modified, LastModified} | UserData],
  