refactor(app.js, auth.js): Extract all auth method to individual modules

lib/web/auth/dropbox/index.js

@@ -0,0 +1,29 @@
+'use strict'
+
+const Router = require('express').Router
+const passport = require('passport')
+const DropboxStrategy = require('passport-dropbox-oauth2').Strategy
+const config = require('../../../config')
+const {setReturnToFromReferer, passportGeneralCallback} = require('../utils')
+
+let dropboxAuth = module.exports = Router()
+
+passport.use(new DropboxStrategy({
+  apiVersion: '2',
+  clientID: config.dropbox.clientID,
+  clientSecret: config.dropbox.clientSecret,
+  callbackURL: config.serverurl + '/auth/dropbox/callback'
+}, passportGeneralCallback))
+
+dropboxAuth.get('/auth/dropbox', function (req, res, next) {
+  setReturnToFromReferer(req)
+  passport.authenticate('dropbox-oauth2')(req, res, next)
+})
+
+// dropbox auth callback
+dropboxAuth.get('/auth/dropbox/callback',
+  passport.authenticate('dropbox-oauth2', {
+    successReturnToOrRedirect: config.serverurl + '/',
+    failureRedirect: config.serverurl + '/'
+  })
+)