Slack was mandatory up until recently. Outline devs have opened it up, but we need to implement our own authentication method (LDAP plugin is for paid Outline licence, for example…). So, wait and see, or test it out by creating à dummy Slack account.
We will have look, thanks!
Try npm install koa-webpack-dev-middleware before running the build.
Disclaimer: I am no Node dev, so I am like you trying to code by mimicking others. 