Currently, ORAS is not able to authenticate docker.io and will return 401 error:

$ oras cp mcr.microsoft.com/mmlspark/spark2.4:1.0.0 docker.io/pengfeizhou/spark2.4:1.0.0
Error: POST "https://registry-1.docker.io/v2/pengfeizhou/spark2.4/blobs/uploads/": unexpected status code 401: unauthorized: authentication required

It requires users to specify registry-1.docker.io to authenticate with DockerHub. I think ORAS should support the most common domain docker.io when interacting with DockerHub.