Add optional mTLS support for client & server

app/cmd/client.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"crypto/sha256"
+	"crypto/tls"
 	"crypto/x509"
 	"encoding/hex"
 	"errors"
@@ -96,10 +97,12 @@ type clientConfigObfs struct {
 }
 
 type clientConfigTLS struct {
-	SNI       string `mapstructure:"sni"`
-	Insecure  bool   `mapstructure:"insecure"`
-	PinSHA256 string `mapstructure:"pinSHA256"`
-	CA        string `mapstructure:"ca"`
+	SNI               string `mapstructure:"sni"`
+	Insecure          bool   `mapstructure:"insecure"`
+	PinSHA256         string `mapstructure:"pinSHA256"`
+	CA                string `mapstructure:"ca"`
+	ClientCertificate string `mapstructure:"clientCertificate"`
+	ClientKey         string `mapstructure:"clientKey"`
 }
 
 type clientConfigQUIC struct {
@@ -294,6 +297,31 @@ func (c *clientConfig) fillTLSConfig(hyConfig *client.Config) error {
 		}
 		hyConfig.TLSConfig.RootCAs = cPool
 	}
+	if c.TLS.ClientCertificate != "" && c.TLS.ClientKey != "" {
+		certLoader := &utils.LocalCertificateLoader{
+			CertFile: c.TLS.ClientCertificate,
+			KeyFile:  c.TLS.ClientKey,
+		}
+		// Try loading the cert-key pair here to catch errors early
+		err := certLoader.InitializeCache()
+		if err != nil {
+			var pathErr *os.PathError
+			if errors.As(err, &pathErr) {
+				if pathErr.Path == c.TLS.ClientCertificate {
+					return configError{Field: "tls.clientCertificate", Err: pathErr}
+				}
+				if pathErr.Path == c.TLS.ClientKey {
+					return configError{Field: "tls.clientKey", Err: pathErr}
+				}
+			}
+			return configError{Field: "tls.clientCertificate", Err: err}
+		}
+		// Use GetClientCertificates so that users can update the cert without restarting the client.
+		hyConfig.TLSConfig.GetClientCertificate = func(*tls.CertificateRequestInfo) (*tls.Certificate, error) {
+			// For simplicity, always respond with the configured client certs, regardless of server requests.
+			return certLoader.GetCertificate(nil)
+		}
+	}
 	return nil
 }
 

app/cmd/client_test.go

@@ -33,10 +33,12 @@ func TestClientConfig(t *testing.T) {
 			},
 		},
 		TLS: clientConfigTLS{
-			SNI:       "another.example.com",
-			Insecure:  true,
-			PinSHA256: "114515DEADBEEF",
-			CA:        "custom_ca.crt",
+			SNI:               "another.example.com",
+			Insecure:          true,
+			PinSHA256:         "114515DEADBEEF",
+			CA:                "custom_ca.crt",
+			ClientCertificate: "client.crt",
+			ClientKey:         "client.key",
 		},
 		QUIC: clientConfigQUIC{
 			InitStreamReceiveWindow:     1145141,

app/cmd/client_test.yaml

@@ -17,6 +17,8 @@ tls:
   insecure: true
   pinSHA256: 114515DEADBEEF
   ca: custom_ca.crt
+  clientCertificate: client.crt
+  clientKey: client.key
 
 quic:
   initStreamReceiveWindow: 1145141

app/cmd/server.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"context"
 	"crypto/tls"
+	"crypto/x509"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -86,6 +87,7 @@ type serverConfigTLS struct {
 	Cert     string `mapstructure:"cert"`
 	Key      string `mapstructure:"key"`
 	SNIGuard string `mapstructure:"sniGuard"` // "disable", "dns-san", "strict"
+	ClientCA string `mapstructure:"clientCA"`
 }
 
 type serverConfigACME struct {
@@ -333,6 +335,18 @@ func (c *serverConfig) fillTLSConfig(hyConfig *server.Config) error {
 		// Use GetCertificate instead of Certificates so that
 		// users can update the cert without restarting the server.
 		hyConfig.TLSConfig.GetCertificate = certLoader.GetCertificate
+		// Client CA
+		if c.TLS.ClientCA != "" {
+			ca, err := os.ReadFile(c.TLS.ClientCA)
+			if err != nil {
+				return configError{Field: "tls.clientCA", Err: err}
+			}
+			cPool := x509.NewCertPool()
+			if !cPool.AppendCertsFromPEM(ca) {
+				return configError{Field: "tls.clientCA", Err: errors.New("failed to parse client CA certificate")}
+			}
+			hyConfig.TLSConfig.ClientCAs = cPool
+		}
 	} else {
 		// ACME
 		dataDir := c.ACME.Dir

app/cmd/server_test.go

@@ -29,6 +29,7 @@ func TestServerConfig(t *testing.T) {
 			Cert:     "some.crt",
 			Key:      "some.key",
 			SNIGuard: "strict",
+			ClientCA: "some_ca.crt",
 		},
 		ACME: &serverConfigACME{
 			Domains: []string{

app/cmd/server_test.yaml

@@ -9,6 +9,7 @@ tls:
   cert: some.crt
   key: some.key
   sniGuard: strict
+  clientCA: some_ca.crt
 
 acme:
   domains:

core/client/client.go

@@ -74,6 +74,7 @@ func (c *clientImpl) connect() (*HandshakeInfo, error) {
 		InsecureSkipVerify:    c.config.TLSConfig.InsecureSkipVerify,
 		VerifyPeerCertificate: c.config.TLSConfig.VerifyPeerCertificate,
 		RootCAs:               c.config.TLSConfig.RootCAs,
+		GetClientCertificate:  c.config.TLSConfig.GetClientCertificate,
 	}
 	quicConfig := &quic.Config{
 		InitialStreamReceiveWindow:     c.config.QUICConfig.InitialStreamReceiveWindow,

core/client/config.go

@@ -1,6 +1,7 @@
 package client
 
 import (
+	"crypto/tls"
 	"crypto/x509"
 	"net"
 	"time"
@@ -92,6 +93,7 @@ type TLSConfig struct {
 	InsecureSkipVerify    bool
 	VerifyPeerCertificate func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error
 	RootCAs               *x509.CertPool
+	GetClientCertificate  func(*tls.CertificateRequestInfo) (*tls.Certificate, error)
 }
 
 // QUICConfig contains the QUIC configuration fields that we want to expose to the user.

core/server/config.go

@@ -2,6 +2,7 @@ package server
 
 import (
 	"crypto/tls"
+	"crypto/x509"
 	"net"
 	"net/http"
 	"sync/atomic"
@@ -101,6 +102,7 @@ func (c *Config) fill() error {
 type TLSConfig struct {
 	Certificates   []tls.Certificate
 	GetCertificate func(info *tls.ClientHelloInfo) (*tls.Certificate, error)
+	ClientCAs      *x509.CertPool
 }
 
 // QUICConfig contains the QUIC configuration fields that we want to expose to the user.

core/server/server.go

@@ -26,14 +26,26 @@ type Server interface {
 	Close() error
 }
 
+func convertToStdTLSConfig(config *Config) *tls.Config {
+	var clientAuth tls.ClientAuthType
+	if config.TLSConfig.ClientCAs != nil {
+		clientAuth = tls.RequireAndVerifyClientCert
+	} else {
+		clientAuth = tls.NoClientCert
+	}
+	return http3.ConfigureTLSConfig(&tls.Config{
+		Certificates:   config.TLSConfig.Certificates,
+		GetCertificate: config.TLSConfig.GetCertificate,
+		ClientCAs:      config.TLSConfig.ClientCAs,
+		ClientAuth:     clientAuth,
+	})
+}
+
 func NewServer(config *Config) (Server, error) {
 	if err := config.fill(); err != nil {
 		return nil, err
 	}
-	tlsConfig := http3.ConfigureTLSConfig(&tls.Config{
-		Certificates:   config.TLSConfig.Certificates,
-		GetCertificate: config.TLSConfig.GetCertificate,
-	})
+	tlsConfig := convertToStdTLSConfig(config)
 	quicConfig := &quic.Config{
 		InitialStreamReceiveWindow:     config.QUICConfig.InitialStreamReceiveWindow,
 		MaxStreamReceiveWindow:         config.QUICConfig.MaxStreamReceiveWindow,