code: def _make_token_async(scopes, service_account_id):
    
    rpc = app_identity.create_rpc()
    app_identity.make_get_access_token_call(rpc, scopes, service_account_id)
    token, expires_at = yield rpc
    raise ndb.Return((token, expires_at))
docs: Get a fresh authentication token.
  
    Args:
      scopes: A list of scopes.
      service_account_id: Internal-use only.
  
    Raises:
      An ndb.Return with a tuple (token, expiration_time) where expiration_time is
      seconds since the epoch.