Oracle Cloud Infrastructure (OCI) supports "instance princpal" authentication.
From
<https://docs.cloud.oracle.com/en-us/iaas/Content/Identity/Tasks/callingservicesfrominstances.htm>:
> After you set up the required resources and policies, an application running
> on an instance can call Oracle Cloud Infrastructure public services, removing
> the need to configure user credentials or a configuration file.
This change adds support to the OCI provider for instance principal
authentication when external-dns is run on an OCI instance (e.g. in OCI OKE).
Existing support for key/fingerprint-based authentication is unchanged.
