How to: Register endpoint
The method returns a new unique subdomain and credentials needed to update your record.
Fulldomain is where you can point your own `_acme-challenge` subdomain CNAME record to.
With the credentials, you can update the TXT response in the service to match the challenge token, later referred as \_\_\_validation\_token\_received\_from\_the\_ca\_\_\_, given out by the Certificate Authority.

**Optional:**: You can POST JSON data to limit the `/update` requests to predefined source networks using CIDR notation.

```POST /register```

#### OPTIONAL Example input
```json
{
    "allowfrom": [
        "192.168.100.1/24",
        "1.2.3.4/32",
        "2002:c0a8:2a00::0/40"
    ]
}
```

```Status: 201 Created```
```json
{
    "allowfrom": [
        "192.168.100.1/24",
        "1.2.3.4/32",
        "2002:c0a8:2a00::0/40"
    ],
    "fulldomain": "8e5700ea-a4bf-41c7-8a77-e990661dcc6a.auth.acme-dns.io",
    "password": "htB9mR9DYgcu9bX_afHF62erXaH2TS7bg9KW3F7Z",
    "subdomain": "8e5700ea-a4bf-41c7-8a77-e990661dcc6a",
    "username": "c36f50e8-4632-44f0-83fe-e070fef28a10"
}
```