Major Description
Currently, proxy.config.http.server_ports allows to configure supported/allowed list of protocols for a given proxy port. The same list gets sent as the advertised protocol list in the NPN/ALPN advertisement.
However, there are situations, where the servers may want the allowed/supported protocol list to be different to the npn advertised list. For example, you may want to allow http/1.0 for clients not supporting npn extensions, but, do not want to advertise http/1.0 in the npn list to prevent clients that support npn extension from picking http/1.0.
As such, I am wondering if we should have a separate control on the npn/alpn advertised protocol list.
If so, please provide comments/suggestions. One straightforward choice is to extend the supported parameters for proxy ports (i.e add another parameter similar to ":proto"), but, it seems like the configuration becomes more and more complex and harder to understand/comprehend.