mod_http_oauth2: Implement the Implicit flow Everyone says this is insecure and bad, but it's also the only thing that makes sense for e.g. pure JavaScript clients, but hey implement this even more complicated thing instead!

---
summary: Store registration events in the audit log
rockspec:
  dependencies:
  - mod_audit
...

This module stores successful user registrations in the audit log provided by
`mod_audit`.