For the api: /beta/repositories/docker/proxy the DockerProxyRepositoryApiRequest HttpClientConnectionAuthenticationAttributes part of the API does not allow the user to simply configure the user and password. Please add the ability to specify the password.
Suggest you file improvement requests to our issue tracker (https://issues.sonatype.org/projects/NEXUS) for leadership analysis. Alternatively, you could post your use case to the parent REST impl story for repositories (https://issues.sonatype.org/browse/NEXUS-15091) so that it’s not forgotten.
I think your point is justified, I didn’t see this addressed in existing tickets (unless the parent ticket intent is to cover “all”).