code: def _token_to_bytes(access_token: AccessToken) -> bytes:
      return f"{access_token.username} {access_token.public_key} {access_token.expiration_time}".encode()
  
file_path: hivemind/tests/test_auth.py
imports: from datetime import datetime, timedelta
  from typing import Optional
  import pytest
  from hivemind.proto import dht_pb2
  from hivemind.proto.auth_pb2 import AccessToken
  from hivemind.utils.auth import AuthRole, AuthRPCWrapper, TokenAuthorizerBase
  from hivemind.utils.crypto import RSAPrivateKey
  from hivemind.utils.logging import get_logger
label_desc: Use image node_id 4 for calling the MockAuthorizer obj's underlying member method code with example usage: obj._token_to_bytes(access_token) and returns: access_token, str, access_token, str, access_token