This can also be done using existing Vaults or Secrets manager. Hashicorp Vault can do this and agents can be instructed to get secrets, which are set without the agent's knowledge. I use these 2 simple scripts with OpenClaw to achieve this, along with time-scoped expiration. The call to vault_get.sh is inside the agent's skill script so that the secrets are not leaked to LLMs or in any trace logs:
vault_get.sh: https://gist.github.com/sathish316/1ca3fe1b124577d1354ee254a...
vault_set.sh: https://gist.github.com/sathish316/1f4e6549a8f85ac5c5ac8a088...
Blog about the full setup for OpenClaw: https://x.com/sathish316/status/2019496552419717390