fix(auth): set JWT token for user/password method

[rodrigo-brito]

I discovered that the new NPM version always set JWT token when auth, and some private registry such as https://github.com/verdaccio/verdaccio, do not support _auth param.

I proposes a flow change:

• Instead of use _auth param, we can fetch a new JWT token and uses it as auth credential.

The login method was ported from NPM CLI project: https://github.com/npm/cli/blob/b46fed75379979a6be86ac72117a90f8ad3b3a99/node_modules/npm-profile/lib/index.js#L111-L191

Ref #61

[donny-dont]

When I started this plugin I used Sinopia as a test target. Eventually moved off of it to NPM Enterprise when Sinopia wasn't being actively maintained. Just making a note that its good to see a healthy fork of it.

I largely haven't used NPM in forever so I don't really have a whole lot of different things to test against. In the present ecosystem is it now just NPM proper, Verdaccio, and Artifactory?

The code itself is fine but the linter is not happy, see https://cloud.drone.io/drone-plugins/drone-npm/41/1/2 , so I think I'm ok with approving this after the build is successful. If it fails the docker steps because of pull limits thats fine but it should definitely get to those steps.

Also I'm asking folks about the versioning and I'd like to tag the master branch before landing this.

[rodrigo-brito]

I largely haven't used NPM in forever so I don't really have a whole lot of different things to test against. In the present ecosystem is it now just NPM proper, Verdaccio, and Artifactory?

I think Github Packages is also used nowadays. I will try to test against these ones.