mod_rest: Support parameters in callback URL E.g. rest_callback_url = "http://myapi.example:5000/api/{kind}/{type}" which results in e.g. requests to /api/message/chat Allows using path routing in web frameworks for dispatch instead of having to pick apart the payload to further dispatch it.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
s2s_whitelist = {
    "example.org",
}
```