Force client hostname when proxying https

Question

I'm using toxiproxy. I'm having this exact issue. Both of the curl solutions mentioned in the issue work (solution a, solution b), but I can't use curl. I need to use the go standard net/http library.

Is there any way to use net/http in such a fashion that I can explicitly tell it what host the proxy is using so it can see that the certificate is valid?

I've tried setting Host and Authority headers on the net/http.Request, but that didn't work.

Details

Toxiproxy output:

proxy=[::]:22002 upstream=maps.googleapis.com:443

My code:

url := "https://localhost:22002/maps/api/geocode/json..."
req, err := http.NewRequest("GET", url, nil)
req.Host = "maps.googleapis.com"
req.Header.Set("Host", "maps.googleapis.com")
res, err := httpClient.Do(req)

Error:

x509: certificate is valid for *.googleapis.com, *.clients6.google.com, *.cloudendpointsapis.com, cloudendpointsapis.com, googleapis.com, not localhost

Answer 1

You need to set the http.Request.Host field so that the http request has the correct header

req.Host = "maps.googleapis.com"

An you also need to set the hostname in the tls.Config.ServerName field for SNI and host name verification.

If you've already configured a transport for your httpClient, you can set it like so:

httpClient.Transport.(*http.Transport).TLSClientConfig = &tls.Config{
    ServerName: "maps.googleapis.com",
}

Or for small programs you can override the default:

http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{
    ServerName: "maps.googleapis.com",
}

Or create a custom transport for your program

var httpTransport = &http.Transport{
    Proxy: http.ProxyFromEnvironment,
    DialContext: (&net.Dialer{
        Timeout:   30 * time.Second,
        KeepAlive: 30 * time.Second,
        DualStack: true,
    }).DialContext,
    MaxIdleConns:          100,
    IdleConnTimeout:       90 * time.Second,
    TLSHandshakeTimeout:   10 * time.Second,
    ExpectContinueTimeout: 1 * time.Second,
    TLSClientConfig: &tls.Config{
        ServerName: "maps.googleapis.com",
    },
}

Just make sure you reuse the Transport, and don't create a new one for each request.