[BUG] If the token is not set in VaultConfig, it will not be set automatically after calling .auth().loginByKubernetes()

[trend-jeff-chu]

Describe the bug
I am not sure whether I implement it correctly, here is what I found:
If the token is not set in VaultConfig (either by specifying explicitly by calling .token("<my_token>"), or getting from environment variable VAULT_TOKEN),
it will not be set automatically after calling .auth().loginByKubernetes("<role>", "<jwt>").
Therefore, it will encounter 403 http error when calling logical().read(xxx)