Intro
The plan is to create a pair of executables (ngrok and ngrokd) that are connected with a self-signed SSL cert. Since the client and server executables are paired, you won't be able to use any other ngrok to connect to this ngrokd, and vice versa.
DNS
Add two DNS records: one for the base domain and one for the wildcard domain. For example, if your base domain is domain.com, you'll need a record for that and for *.domain.com.