Add a registry via the API?

Rancher 1.x
4

So I am able to create a registry

curl -u “${CATTLE_ACCESS_KEY}:${CATTLE_SECRET_KEY}”
-X POST
-H ‘Accept: application/json’
-H ‘Content-Type: application/json’
-d ‘{“name”:“Test”, “serverAddress”:“index.docker.io”}’
‘http://192.168.33.11:8080/v1/projects/1a5/registries’

It shows up in my list of registries. But I can’t figure out how configure Dockerhub credentials? Would that be another API call? I apologize, I’m not very good with API’s.