1. Create your app with medium: https://medium.com/me/applications
2. Create your medium-config.json. It needs to contain:

  {
    "client_id": "YOUR_CLIENT_ID"
  , "client_secret": "YOUR_SECRET"
  , "redirect_url": "http://dillinger.io/oauth/medium"
  , "callback_url": "http://dillinger.io/"
  }    

The values for client_id and client_secret can be obtained on the Medium app page.

For redirect_url, use http://yoursite/oauth/medium (or supply your own callback URL if you've created a custom route).

Set the following environment variables if adding medium-config.json may present a challenge (when deploying on Heroku for example)

  medium_client_id=YOUR_KEY
  medium_client_secret=YOUR_SECRET
  medium_callback_url=YOUR_CALLBACK_URL
  medium_redirect_url=YOUR_REDIRECT_URL