code: public boolean expiresWithin(int minutes) {
  
          DateTime dateToCheck = DateTime.now().plusMinutes(minutes);
          boolean isExpired = dateToCheck.isAfter(this.expirationDate);
  
          return isExpired;
      }
docs: Helper method that returns true, if the token is expired in the given
  number of minutes (starting from the current point of time).
  
  @param minutes
  @return Whether or not the token expires within the given number of
  minutes.