mod_roster_command: Fix subscription when the "user JID" is a bare domain. Do not attempt to update the roster when the user is bare domain (e.g. a component), since they don't have rosters and the attempt results in an error: $ prosodyctl mod_roster_command subscribe proxy.example.com contact@example.com xxxxxxxxxxFailed to execute command: Error: /usr/lib/prosody/core/rostermanager.lua:104: attempt to concatenate local 'username' (a nil value) stack traceback: /usr/lib/prosody/core/rostermanager.lua:104: in function 'load_roster' /usr/lib/prosody/core/rostermanager.lua:305: in function 'set_contact_pending_out' mod_roster_command.lua:44: in function 'subscribe'

---
labels:
- 'Type-S2SAuth'
---

Introduction
============

[PKIX over Secure HTTP (POSH)][rfc7711] describes a method of
securely delegating a domain to a hosting provider, without that hosting
provider needing keys and certificates covering the hosted domain.

# Validating

This module performs POSH validation of other servers. It is *not*
needed to delegate your own domain.

# Delegation

You can generate the JSON delegation file from a certificate by running
`prosodyctl mod_s2s_auth_posh /path/to/example.crt`. This file needs to
be served at `https://example.com/.well-known/posh/xmpp-server.json`.