code: def get_access_token(self, http=None):
          
          if not self.access_token or self.access_token_expired:
              if not http:
                  http = transport.get_http_object()
              self.refresh(http)
          return AccessTokenInfo(access_token=self.access_token,
                                 expires_in=self._expires_in())
docs: Return the access token and its expiration information.
  
          If the token does not exist, get one.
          If the token expired, refresh it.