Option for Bearer authentication

[liamkirwan]

Hi, I'm using this library with instances of Jenkins deployed in Openshift, that support OAuth integration with the cluster and token auth via their login plugin.

This library works well for my needs, but assumes you are either using basic auth or a personal access token (or none at all). In a scenario where we have an ApiToken but no username, we can send the token with "Authorization = Bearer XXXX".

The patch for this is simple and I've tested against my environment, would you be willing to take a PR for this?