code: def _set_token_expiration_time(self, expires_in):
          
          self.token_expiration_time = dt.datetime.utcnow() + \
              dt.timedelta(0, expires_in)
docs: Saves the token expiration time by adding the 'expires in' parameter
          to the current datetime (in utc).
  
          Parameters
          ----------
          expires_in : int
              number of seconds from the time of the request until expiration
  
          Returns
          -------
          nothing
              saves expiration time in self.token_expiration_time as
              datetime.datetime