Insert custom HTTP header determined by VS protocol

There are potentially two problems:

1. You've defined a local variable called "proto", but then accessing it as "PROTO". TCL is case sensitive.

2. I've found that many versions of IIS don't like headers with underscores in them. It will natively replace dashes with underscores, but doesn't seem to like it when the header names arrive with underscores.

Try this:

when CLIENT_ACCEPTED {
    switch [TCP::local_port] {
        "443" {
            set proto "https"
        }
        "80" {
            set proto "http"
        }
    }
}
when HTTP_REQUEST {
    HTTP::header insert VS-HTTP-PROTO $proto
}