code: def find_by_token(self, token, salt=None, max_age=None):
          
          model = current_app.features.models[self.options["model"]]
          try:
              id = self.token_serializer.loads(token, salt=salt, max_age=max_age)
          except BadSignature:
              return None
          if id is None:
              return None
          return self.find_by_id(id)
docs: Loads a user instance identified by the token generated using generate_user_token()