a8n: Support more than just NPM credentials

Created by: ryanslade

From RFC 73

See the list of other possible credential types here: https://docs.google.com/document/d/143FIe1Tak4_YPPuOuEzuobTQW09ZU85WfOCdZkNwIVQ/edit#bookmark=id.o2rmxw4xn7qp