feat: Move to passport for authentication (#1934)

- Added `accountProvisioner`
- Move authentication to use passport strategies
- Make authentication more pluggable
- Change language of services -> providers

closes #1120

server/auth/README.md

@@ -0,0 +1,12 @@
+# Authentication Providers
+
+A new auth provider can be added with the addition of a single file in this
+folder, and (optionally) a matching logo in `/app/components/AuthLogo/index.js`
+that will appear on the signin button.
+
+Auth providers generally use [Passport](http://www.passportjs.org/) strategies,
+although they can use any custom logic if needed. See the `google` auth provider for the cleanest example of what is required – some rules:
+
+- The strategy name _must_ be lowercase
+- The stragegy _must_ call the `accountProvisioner` command in the verify callback
+- The auth file _must_ export a `config` object with `name` and `enabled` keys