question: is the original authority available with a host rewrite?

I'm trying to add the original destination (authority) of a request via an access log, or even an additional request header before it gets rewritten for the upstream cluster request. Is this information available somewhere?

An access log with... still logs the rewritten host.

```
action.Route.HostRewriteSpecifier = &envoyroute.RouteAction_HostRewrite{
HostRewrite: "my-new-upstream-host,
}
```
```
"req_host": "%REQ(:AUTHORITY)%"
```

We can use `%REQ(X-ENVOY-ORIGINAL-PATH?:PATH)%` for the original path. Is there something like that for the **original authority**?