@VisibleForTesting
    static String getOriginalHost(Headers headers, String serverName) throws URISyntaxException {
        String xForwardedHost = headers.getFirst(HttpHeaderNames.X_FORWARDED_HOST);
        if (xForwardedHost != null) {
            return xForwardedHost;
        }
        Pair<String, Integer> host = parseHostHeader(headers);
        if (host.first() != null) {
            return host.first();
        }
        return serverName;
    }
The originally request host. This will NOT include port.

The Host header may contain port, but in this method we strip it out for consistency - use the
getOriginalPort method for that.
zuul-core/src/main/java/com/netflix/zuul/message/http/HttpRequestMessageImpl.java