I surround a bat 'npm publish' with a nodejs that contains a configuration id that specifies a registry and a credential.  This creates a config file in the workspace@tmp folder with the following entries:

registry = http:/my-local-nexus.company.com:8081/repository/npm-hosted/
always-auth = true
_auth = <huge base64 string>

at the end of the publish I get the following:

npm ERR! code E401
npm ERR! Unable to authenticate, need: BASIC realm="Sonatype Nexus Repository Manager"