isTimedout method
Returns true if the session is timed out
Implementation
bool isTimedout(User user) {
if (activityTimestamp == -1) {
return false;
}
int timeoutAt = user.rememberFor24h
? activityTimestamp + _timeout24h
: activityTimestamp + _timeout15m;
return DateTime.now().millisecondsSinceEpoch > timeoutAt;
}