This module handles the callback from Untappd's Oauth signin. It exchanges the auth code for a token and redirects to the main app.
Your instance of the Untappd for Hootsuite app should have a "Sign into Untappd" link which sends the user directly to Untappd's Oauth endpoint. That endpoint will complete and forward the user back to this service's /callback endpoint. The endpoint exchanges the temporary token for full credentials. For now, the user is then redirected to app.untappdforhootsuite.com with the full token as a query parameter.
The long-term plan is to have the tokens stored in a DB shared between this service and the main app so that the credentials are not exposed to the user.