All endpoints require the userid (as 48-char lowercase hex string).
Use the Authorization header for this.

Shown are the expected responses, all errors return {"error": "human-readable reason"}

|- domains : {} -> ["...ip6.arpa": {"nameservers": ["..."]}]
|- moveTo  : {"domains": ["...ip6.arpa"], "to": "3498de37.."} -> {}
|- register: {} -> {"domain": "...ip6.arpa"} 
|- remove  : {"domain": "...ip6.arpa"} -> {}