code: func resolveTLSConfig(transport http.RoundTripper) *tls.Config {
  	switch tr := transport.(type) {
  	case *http.Transport:
  		return tr.TLSClientConfig
  	default:
  		return nil
  	}
  }
docs: // resolveTLSConfig attempts to resolve the TLS configuration from the
  // RoundTripper.