mod_http_oauth2: Implement RFC 8628 Device Authorization Grant Meant for devices without easy access to a web browser, such as refrigerators and toasters, which definitely need to be running OAuth-enabled XMPP clients! Could be used for CLI tools that might have trouble running a http server needed for the authorization code flow.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```