@jack Now the former does not require "mutual understanding" of terms; whoever is the proxy knows what is and isn't allowed and simply forwards or doesn't. (However, "shortening" is an option so that server A both does not have to "proxy" to server B; this would require setting up an equivalent proxy back on server B again, which requires that server A and B can negotiate what that attenuation is.)
In the case of certificate ocaps, then there does require some mutual terminology understanding