code: def is_expired_token(self, client):
          
          if 'expires' not in client:
              return True
  
          expires = dateutil.parser.parse(client['expires'])
          if expires < datetime.datetime.now():
              return True
  
          return False
docs: For a given client will test whether or not the token
          has expired.
  
          This is for testing a client object and does not look up
          from client_id.  You can use _get_client_from_cache() to
          lookup a client from client_id.