code: def access_token_expired(self):
          
          if self.invalid:
              return True
  
          if not self.token_expiry:
              return False
  
          now = _UTCNOW()
          if now >= self.token_expiry:
              logger.info('access_token is expired. Now: %s, token_expiry: %s',
                          now, self.token_expiry)
              return True
          return False
docs: True if the credential is expired or invalid.
  
          If the token_expiry isn't set, we assume the token doesn't expire.