feat: check if there's a SNIConfig available for the provider and use…

… it if there's a enabled SNIConfig; also adding function for verifying the certificate

direct.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"math/rand"
+	"math/rand/v2"
 	"net"
 	"net/http"
 	"net/url"
@@ -356,7 +356,7 @@ dialLoop:
 		// We do the full TLS connection here because in practice the domains at a given IP
 		// address can change frequently on CDNs, so the certificate may not match what
 		// we expect.
-		conn, retriable, err := d.doDial(&m.Masquerade)
+		conn, retriable, err := d.doDial(m)
 		masqueradeGood := func(good bool) bool {
 			if good {
 				m.markSucceeded()
@@ -378,7 +378,7 @@ dialLoop:
 	return nil, nil, nil, errors.New("could not dial any masquerade?")
 }
 
-func (d *direct) doDial(m *Masquerade) (conn net.Conn, retriable bool, err error) {
+func (d *direct) doDial(m *masquerade) (conn net.Conn, retriable bool, err error) {
 	op := ops.Begin("dial_masquerade")
 	defer op.End()
 	op.Set("masquerade_domain", m.Domain)
@@ -410,7 +410,7 @@ func (d *direct) doDial(m *Masquerade) (conn net.Conn, retriable bool, err error
 	return
 }
 
-func (d *direct) dialServerWith(m *Masquerade) (net.Conn, error) {
+func (d *direct) dialServerWith(m *masquerade) (net.Conn, error) {
 	tlsConfig := d.frontingTLSConfig(m)
 	dialTimeout := 10 * time.Second
 	sendServerNameExtension := false
@@ -436,9 +436,51 @@ func (d *direct) dialServerWith(m *Masquerade) (net.Conn, error) {
 	return conn, err
 }
 
+func (d *direct) verifyPeerCertificate(domain string, rawCerts [][]byte, _ [][]*x509.Certificate) error {
+	if len(rawCerts) == 0 {
+		return errors.New("no certificates provided")
+	}
+	cert, err := x509.ParseCertificate(rawCerts[0])
+	if err != nil {
+		return err
+	}
+	opts := x509.VerifyOptions{
+		Roots:         d.certPool,
+		CurrentTime:   time.Now(),
+		DNSName:       domain,
+		Intermediates: x509.NewCertPool(),
+	}
+	for i := 1; i < len(rawCerts); i++ {
+		intermediate, err := x509.ParseCertificate(rawCerts[i])
+		if err != nil {
+			return err
+		}
+		opts.Intermediates.AddCert(intermediate)
+	}
+	_, err = cert.Verify(opts)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // frontingTLSConfig builds a tls.Config for dialing the fronting domain. This is to establish the
 // initial TCP connection to the CDN.
-func (d *direct) frontingTLSConfig(m *Masquerade) *tls.Config {
+func (d *direct) frontingTLSConfig(m *masquerade) *tls.Config {
+	provider := d.providers[m.ProviderID]
+	if provider.SNIConfig.UseArbitrarySNIs {
+		randomSNIIndex := rand.IntN(len(provider.SNIConfig.ArbitrarySNIs))
+		sniDomain := provider.SNIConfig.ArbitrarySNIs[randomSNIIndex]
+		return &tls.Config{
+			InsecureSkipVerify: true,
+			VerifyPeerCertificate: func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {
+				return d.verifyPeerCertificate(m.Domain, rawCerts, verifiedChains)
+			},
+			ServerName: sniDomain,
+			RootCAs:    d.certPool,
+		}
+	}
 	return &tls.Config{
 		ServerName: m.Domain,
 		RootCAs:    d.certPool,