Golang ReverseProxy with Apache2 SNI/Hostname error - ssl

Question

i am writing my own ReverseProxy in Go.The ReverseProxy should connect my go-webserver and my apache2 webserver. But when I run my reverseproxy on another IP-Adress then my Apache2 webserver I got following error in my apache-logfile, when the reverseproxy sends the request to apache.
"Hosname xxxx provided via sni and hostname xxxx2 provided via http are different"
My Reverse Proxy and apache-webserver running on https.
Here some code:
func (p *Proxy) directorApache(req *http.Request) {
mainServer := fmt.Sprintf("%s:%d", Config.HostMain, Config.PortMain)
req.URL.Scheme = "https"
req.URL.Host = mainServer
}
func (p *Proxy) directorGo(req *http.Request) {
goServer := fmt.Sprintf("%s:%d", Config.GoHost, Config.GoPort)
req.URL.Scheme = "http"
req.URL.Host = goServer
}
func (p *Proxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
fmt.Println(req.URL.Path)
if p.isGoRequest(req) {
fmt.Println("GO")
p.goProxy.ServeHTTP(rw, req)
return
}
p.httpProxy.ServeHTTP(rw, req)
}
func main() {
var configPath = flag.String("conf", "./configReverse.json", "Path to the Json config file.")
flag.Parse()
proxy := New(*configPath)
cert, err := tls.LoadX509KeyPair(Config.PathCert, Config.PathPrivateKey)
if err != nil {
log.Fatalf("server: loadkeys: %s", err)
}
config := tls.Config{InsecureSkipVerify: true, Certificates: []tls.Certificate{cert}}
listener, err := net.Listen("tcp",
net.JoinHostPort(proxy.Host, strconv.Itoa(proxy.Port)))
if err != nil {
log.Fatalf("server: listen: %s", err)
}
log.Printf("server: listening on %s")
proxy.listener = tls.NewListener(listener, &config)
serverHTTPS := &http.Server{
Handler: proxy.mux,
TLSConfig: &config,
}
if err := serverHTTPS.Serve(proxy.listener); err != nil {
log.Fatal("SERVER ERROR:", err)
}
}
Perhaps someone has a idea about that issue.

Answer 1

Short example
Say you're starting an HTTP request to https://your-proxy.local. Your request handler takes the http.Request struct and rewrites its URL field to https://your-apache-backend.local.
What you have not considered, is that the original HTTP request also contained a Host header (Host: your-proxy.local). When passing that same request to http://your-apache-backend.local, the Host header in that request still says Host: your-proxy.local. And that's what Apache is complaining about.
Explanation
As you're using TLS with Server Name Indication (SNI), the request hostname will not only be used for DNS resolution, but also to select the SSL certificate that should be used to establish the TLS connection. The HTTP 1.1 Host header on the other hand is used to distinguish several virtual hosts by Apache. Both names must match. This issue is also mentioned in the Apache HTTPD wiki:
SNI/Request hostname mismatch, or SNI provides hostname and request doesn't.
This is a browser bug. Apache will reject the request with a 400-type error.
Solution
Also rewrite the Host header. If you want to preserve the original Host header, you can store it in an X-Forwarded-Host header (that's a non-standard header, but it's widely used in reverse proxies):
func (p *Proxy) directorApache(req *http.Request) {
mainServer := fmt.Sprintf("%s:%d", Config.HostMain, Config.PortMain)
req.URL.Scheme = "https"
req.URL.Host = mainServer
req.Header.Set("X-Forwarded-Host", req.Header().Get("Host"))
req.Host = mainServer
}