mod_http_oauth2: Fill in some client metadata defaults Explicit > Implicit Maybe we should actually use these for something as well? :) It's is somewhat an open question of how strictly we should enforce things in the client metadata given that it is somewhat extensible. Especially some of these enum fields which have corresponding IANA registries.

Generate a DNS UPDATE order in format suitable for `nsupdate` based on
current port configuration.

Example output:

```
$ prosodyctl mod_dnsupdate -d example.com -t xmpp.example.com example.com
zone example.com
server ns1.example.com
ttl 3600
add _xmpp-client._tcp.example.com IN SRV 1 1 5222
add _xmpp-server._tcp.example.com IN SRV 1 1 5269
```