Replace VNC JWT auth with a Noise_IK handshake bound to ACL-pushed pubkeys

client/vnc/server/server.go

@@ -3,6 +3,8 @@
 package server
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"crypto/subtle"
 	"encoding/binary"
@@ -13,16 +15,15 @@ import (
 	"io"
 	"net"
 	"net/netip"
-	"strings"
 	"sync"
 	"time"
 
-	gojwt "github.com/golang-jwt/jwt/v5"
+	"github.com/flynn/noise"
 	log "github.com/sirupsen/logrus"
+	"golang.org/x/crypto/curve25519"
 	"golang.zx2c4.com/wireguard/tun/netstack"
 
 	sshauth "github.com/netbirdio/netbird/client/ssh/auth"
-	nbjwt "github.com/netbirdio/netbird/shared/auth/jwt"
 )
 
 // Connection modes sent by the client in the session header.
@@ -35,11 +36,7 @@ const (
 // stable so clients can branch on them without parsing free text.
 // Format: "CODE: human message".
 const (
-	RejectCodeJWTMissing    = "AUTH_JWT_MISSING"
-	RejectCodeJWTExpired    = "AUTH_JWT_EXPIRED"
-	RejectCodeJWTInvalid    = "AUTH_JWT_INVALID"
 	RejectCodeAuthForbidden = "AUTH_FORBIDDEN"
-	RejectCodeAuthConfig    = "AUTH_CONFIG"
 	RejectCodeSessionError  = "SESSION_ERROR"
 	RejectCodeCapturerError = "CAPTURER_ERROR"
 	RejectCodeUnsupportedOS = "UNSUPPORTED"
@@ -56,6 +53,21 @@ const EnvVNCDisableDownscale = "NB_VNC_DISABLE_DOWNSCALE"
 // enough to coalesce bursty multi-session requests. 16 ms ~= 60 fps.
 const freshWindow = 16 * time.Millisecond
 
+// maxConcurrentVNCConns caps in-flight VNC connections. Each accepted
+// connection consumes a handler goroutine, a tracking entry, and (after
+// handshake) capturer/encoder resources, so an unauthenticated peer that
+// dials in a tight loop could otherwise grow memory without bound. The
+// limit covers the entire accept→handshake→session window; a slot is
+// released only when the handler returns.
+const maxConcurrentVNCConns = 64
+
+// maxFramebufferDim caps the screen dimensions accepted from a capturer.
+// RFB serialises width/height as u16, and the encoder allocates per-frame
+// buffers proportional to width*height*4. 8192 keeps width*height*4 well
+// under 2^31 so int math doesn't overflow on 32-bit builds, and is large
+// enough to cover real-world multi-monitor desktops.
+const maxFramebufferDim = 8192
+
 // ScreenCapturer grabs desktop frames for the VNC server.
 type ScreenCapturer interface {
 	// Width returns the current screen width in pixels.
@@ -120,26 +132,22 @@ type InputInjector interface {
 	TypeText(text string)
 }
 
-// JWTConfig holds JWT validation configuration for VNC auth.
-type JWTConfig struct {
-	Issuer       string
-	KeysLocation string
-	MaxTokenAge  int64
-	Audiences    []string
-}
-
 // connectionHeader is sent by the client before the RFB handshake to specify
 // the VNC session mode and authenticate.
 type connectionHeader struct {
 	mode     byte
 	username string
-	jwt      string
+	// clientStatic is the client's static X25519 public key learned from
+	// the Noise handshake. Populated when identityVerified is true.
+	clientStatic []byte
 	// sessionID is the Windows session ID; 0 selects the console session.
 	sessionID uint32
 	// width and height request the virtual display geometry for session mode.
 	// Zero means use the default.
 	width  uint16
 	height uint16
+	// identityVerified is true when the Noise_IK handshake completed.
+	identityVerified bool
 }
 
 // Server is the embedded VNC server that listens on the WireGuard interface.
@@ -170,13 +178,16 @@ type Server struct {
 	ctx          context.Context
 	cancel       context.CancelFunc
 	vmgr         virtualSessionManager
-	jwtConfig    *JWTConfig
-	jwtValidator *nbjwt.Validator
-	jwtExtractor *nbjwt.ClaimsExtractor
-	authorizer   *sshauth.Authorizer
-	netstackNet  *netstack.Net
+	authorizer  *sshauth.Authorizer
+	netstackNet *netstack.Net
 	// agentToken holds the raw token bytes for agent-mode auth.
 	agentToken []byte
+	// identityKey is the daemon's static X25519 private key used in the
+	// Noise_IK handshake. Nil disables the handshake.
+	identityKey []byte
+	// identityPublic is the matching X25519 public key, derived once at
+	// construction to avoid recomputing per handshake.
+	identityPublic []byte
 
 	sessionsMu   sync.Mutex
 	sessionSeq   uint64
@@ -188,6 +199,17 @@ type Server struct {
 	// closeActiveSessions iterates this set so Stop() can interrupt
 	// handshaking peers, not just post-handshake sessions.
 	acceptedConns map[net.Conn]struct{}
+	// connAuth holds the verified Noise_IK identity tied to each accepted
+	// connection so a later UpdateVNCAuth call can revoke live sessions
+	// whose authorization no longer holds. Populated by registerConnAuth
+	// once authenticateSession succeeds; absent entries (e.g. disableAuth
+	// or pre-handshake conns) are skipped at revocation time.
+	connAuth map[net.Conn]connAuthInfo
+
+	// connSem caps concurrent accepted connections (handshake + session).
+	// Buffered with maxConcurrentVNCConns slots; accept loops try-acquire
+	// before spawning a handler and release on handler return.
+	connSem chan struct{}
 
 	// sessionRecorder, when non-nil, receives a SessionTick periodically
 	// during each VNC session and on session close. The engine wires
@@ -195,12 +217,24 @@ type Server struct {
 	sessionRecorder func(SessionTick)
 }
 
+// connAuthInfo captures the Noise_IK-verified identity bound to a live
+// connection so policy updates can re-check it and close sessions whose
+// authorization was revoked. clientStatic is empty when auth was disabled
+// for this connection, which signals that revocation does not apply.
+type connAuthInfo struct {
+	clientStatic []byte
+	mode         byte
+	username     string
+}
+
 // ActiveSessionInfo describes a currently connected VNC client.
 type ActiveSessionInfo struct {
 	RemoteAddress string
 	Mode          string
 	Username      string
-	JWTUsername   string
+	// UserID is the authenticated session identity (hashed user ID from
+	// the Noise_IK static-key registration), empty when auth is disabled.
+	UserID string
 }
 
 // vncSession provides capturer and injector for a virtual display session.
@@ -220,19 +254,31 @@ type virtualSessionManager interface {
 	StopAll()
 }
 
-// New creates a VNC server with the given screen capturer and input injector.
-// Authentication uses a JWT supplied by the client in the connection
-// header; the protocol-level VNC password scheme is not supported.
-func New(capturer ScreenCapturer, injector InputInjector) *Server {
-	return &Server{
+// New creates a VNC server. identityKey is the 32-byte X25519 private
+// key used by the daemon in the Noise_IK handshake; nil disables auth.
+// The protocol-level VNC password scheme is not supported.
+func New(capturer ScreenCapturer, injector InputInjector, identityKey []byte) *Server {
+	s := &Server{
 		capturer:      capturer,
 		injector:      injector,
+		identityKey:   identityKey,
 		authorizer:    sshauth.NewAuthorizer(),
 		log:           log.WithField("component", "vnc-server"),
 		sessions:      make(map[uint64]ActiveSessionInfo),
 		sessionConns:  make(map[uint64]net.Conn),
 		acceptedConns: make(map[net.Conn]struct{}),
+		connAuth:      make(map[net.Conn]connAuthInfo),
+		connSem:       make(chan struct{}, maxConcurrentVNCConns),
 	}
+	if len(identityKey) == 32 {
+		pub, err := curve25519.X25519(identityKey, curve25519.Basepoint)
+		if err == nil {
+			s.identityPublic = pub
+		} else {
+			s.log.Warnf("derive identity public key: %v", err)
+		}
+	}
+	return s
 }
 
 // ActiveSessions returns a snapshot of currently connected VNC clients.
@@ -292,9 +338,75 @@ func (s *Server) trackConn(c net.Conn) {
 func (s *Server) untrackConn(c net.Conn) {
 	s.sessionsMu.Lock()
 	delete(s.acceptedConns, c)
+	delete(s.connAuth, c)
 	s.sessionsMu.Unlock()
 }
 
+// registerConnAuth records the verified Noise_IK identity for a live
+// connection so UpdateVNCAuth can later revoke it if policy changes.
+// No-op when auth is disabled (e.g. agent-mode loopback connections).
+func (s *Server) registerConnAuth(c net.Conn, header *connectionHeader) {
+	if s.disableAuth || header == nil || len(header.clientStatic) != 32 {
+		return
+	}
+	s.sessionsMu.Lock()
+	s.connAuth[c] = connAuthInfo{
+		clientStatic: append([]byte(nil), header.clientStatic...),
+		mode:         header.mode,
+		username:     header.username,
+	}
+	s.sessionsMu.Unlock()
+}
+
+// tryAcquireConnSlot returns true when a connection slot was successfully
+// reserved. Releases must pair with releaseConnSlot. Returns false when
+// the cap is already saturated; callers must close the connection.
+func (s *Server) tryAcquireConnSlot() bool {
+	select {
+	case s.connSem <- struct{}{}:
+		return true
+	default:
+		return false
+	}
+}
+
+func (s *Server) releaseConnSlot() {
+	select {
+	case <-s.connSem:
+	default:
+	}
+}
+
+// revokeUnauthorizedSessions closes every live connection whose Noise-
+// verified identity no longer authenticates under the current authorizer
+// configuration. Called by UpdateVNCAuth after the new policy is applied.
+func (s *Server) revokeUnauthorizedSessions() {
+	if s.disableAuth {
+		return
+	}
+	s.sessionsMu.Lock()
+	victims := make([]net.Conn, 0)
+	for c, info := range s.connAuth {
+		if len(info.clientStatic) != 32 {
+			continue
+		}
+		hdr := &connectionHeader{
+			identityVerified: true,
+			clientStatic:     info.clientStatic,
+			mode:             info.mode,
+			username:         info.username,
+		}
+		if _, err := s.authenticateSession(hdr); err != nil {
+			victims = append(victims, c)
+			s.log.Infof("revoking VNC session from %s: %v", c.RemoteAddr(), err)
+		}
+	}
+	s.sessionsMu.Unlock()
+	for _, c := range victims {
+		_ = c.Close()
+	}
+}
+
 // SetServiceMode enables proxy-to-agent mode for Windows service operation.
 func (s *Server) SetServiceMode(enabled bool) {
 	s.serviceMode = enabled
@@ -308,16 +420,6 @@ func (s *Server) SetSessionRecorder(recorder func(SessionTick)) {
 	s.sessionRecorder = recorder
 }
 
-// SetJWTConfig configures JWT authentication for VNC connections.
-// Pass nil to disable JWT (public mode).
-func (s *Server) SetJWTConfig(config *JWTConfig) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.jwtConfig = config
-	s.jwtValidator = nil
-	s.jwtExtractor = nil
-}
-
 // SetDisableAuth disables authentication entirely.
 func (s *Server) SetDisableAuth(disable bool) {
 	s.disableAuth = disable
@@ -346,13 +448,14 @@ func (s *Server) SetNetstackNet(n *netstack.Net) {
 	s.netstackNet = n
 }
 
-// UpdateVNCAuth updates the fine-grained authorization configuration.
+// UpdateVNCAuth updates the fine-grained authorization configuration and
+// closes any live session whose identity no longer authenticates under
+// the new policy. Revocation is event-driven: there is no periodic
+// re-check, so a session stays open until either the next UpdateVNCAuth
+// call or normal disconnect.
 func (s *Server) UpdateVNCAuth(config *sshauth.Config) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.jwtValidator = nil
-	s.jwtExtractor = nil
 	s.authorizer.Update(config)
+	s.revokeUnauthorizedSessions()
 }
 
 // Start begins listening for VNC connections on the given address.
@@ -463,9 +566,15 @@ func (s *Server) acceptLoop() {
 			continue
 		}
 
+		if !s.tryAcquireConnSlot() {
+			s.log.Warnf("rejecting VNC connection from %s: %d concurrent connections in flight", conn.RemoteAddr(), maxConcurrentVNCConns)
+			_ = conn.Close()
+			continue
+		}
 		enableTCPKeepAlive(conn, s.log)
 		s.trackConn(conn)
 		go func(c net.Conn) {
+			defer s.releaseConnSlot()
 			defer s.untrackConn(c)
 			s.handleConnection(c)
 		}(conn)
@@ -565,16 +674,17 @@ func (s *Server) handleConnection(conn net.Conn) {
 	if !s.verifyAgentToken(conn, connLog) {
 		return
 	}
-	header, err := readConnectionHeader(conn)
+	header, err := s.readConnectionHeader(conn)
 	if err != nil {
 		connLog.Warnf("read connection header: %v", err)
 		conn.Close()
 		return
 	}
-	connLog, jwtUserID, ok := s.authorizeJWT(conn, header, connLog)
+	connLog, sessionUserID, ok := s.authorizeSession(conn, header, connLog)
 	if !ok {
 		return
 	}
+	s.registerConnAuth(conn, header)
 
 	capturer, injector, sessionCleanup, ok := s.acquireSessionResources(conn, header, &connLog)
 	if !ok {
@@ -586,7 +696,7 @@ func (s *Server) handleConnection(conn net.Conn) {
 		RemoteAddress: conn.RemoteAddr().String(),
 		Mode:          modeString(header.mode),
 		Username:      header.username,
-		JWTUsername:   jwtUserID,
+		UserID:        sessionUserID,
 	}, conn)
 	defer s.removeSession(sessionID)
 
@@ -596,13 +706,20 @@ func (s *Server) handleConnection(conn net.Conn) {
 		return
 	}
 
+	w, h := capturer.Width(), capturer.Height()
+	if w <= 0 || h <= 0 || w > maxFramebufferDim || h > maxFramebufferDim {
+		rejectConnection(conn, codeMessage(RejectCodeCapturerError, fmt.Sprintf("framebuffer dimensions out of range: %dx%d", w, h)))
+		connLog.Warnf("rejecting session: framebuffer %dx%d outside [1, %d]", w, h, maxFramebufferDim)
+		return
+	}
+
 	conn = newMetricsConn(conn, s.sessionRecorder)
 	sess := &session{
 		conn:     conn,
 		capturer: capturer,
 		injector: injector,
-		serverW:  capturer.Width(),
-		serverH:  capturer.Height(),
+		serverW:  w,
+		serverH:  h,
 		log:      connLog,
 	}
 	sess.serve()
@@ -615,25 +732,6 @@ func codeMessage(code, msg string) string {
 	return code + ": " + msg
 }
 
-// jwtErrorCode maps a JWT auth error to a stable reject code.
-func jwtErrorCode(err error) string {
-	if err == nil {
-		return RejectCodeJWTInvalid
-	}
-	if errors.Is(err, nbjwt.ErrTokenExpired) {
-		return RejectCodeJWTExpired
-	}
-	msg := err.Error()
-	switch {
-	case strings.Contains(msg, "JWT required but not provided"):
-		return RejectCodeJWTMissing
-	case strings.Contains(msg, "authorize") || strings.Contains(msg, "not authorized"):
-		return RejectCodeAuthForbidden
-	default:
-		return RejectCodeJWTInvalid
-	}
-}
-
 // rejectConnection sends a minimal RFB handshake with a security failure
 // reason, so VNC clients display the error message instead of a generic
 // "unexpected disconnect."
@@ -658,105 +756,57 @@ func rejectConnection(conn net.Conn, reason string) {
 	_, _ = conn.Write(buf)
 }
 
-const defaultJWTMaxTokenAge = 10 * 60 // 10 minutes
-
-// authenticateJWT validates the JWT from the connection header and checks
-// authorization. For attach mode, just checks membership in the authorized
-// user list. For session mode, additionally validates the OS user mapping.
-func (s *Server) authenticateJWT(header *connectionHeader) (string, error) {
-	if header.jwt == "" {
-		return "", fmt.Errorf("JWT required but not provided")
+// authenticateSession resolves the Noise-verified client static public
+// key to a hashed user identity via the authorizer, and checks OS-user
+// mapping for session mode. Returns the hashed user identity on success.
+func (s *Server) authenticateSession(header *connectionHeader) (string, error) {
+	if !header.identityVerified {
+		return "", fmt.Errorf("identity proof missing")
+	}
+	if len(header.clientStatic) != 32 {
+		return "", fmt.Errorf("client static key missing")
 	}
 
-	s.mu.Lock()
-	if err := s.ensureJWTValidator(); err != nil {
-		s.mu.Unlock()
-		return "", fmt.Errorf("initialize JWT validator: %w", err)
-	}
-	validator := s.jwtValidator
-	extractor := s.jwtExtractor
-	s.mu.Unlock()
-
-	token, err := validator.ValidateAndParse(context.Background(), header.jwt)
+	userIDHash, err := s.authorizer.LookupSessionKey(header.clientStatic)
 	if err != nil {
-		return "", fmt.Errorf("validate JWT: %w", err)
+		return "", fmt.Errorf("lookup session pubkey: %w", err)
 	}
 
-	if err := s.checkTokenAge(token); err != nil {
-		return "", err
+	osUser := "*"
+	if header.mode == ModeSession {
+		osUser = header.username
 	}
-
-	userAuth, err := extractor.ToUserAuth(token)
-	if err != nil {
-		return "", fmt.Errorf("extract user from JWT: %w", err)
+	if _, err := s.authorizer.AuthorizeOSUserBySessionKey(userIDHash, osUser); err != nil {
+		return "", fmt.Errorf("authorize OS user %q: %w", osUser, err)
 	}
-	if userAuth.UserId == "" {
-		return "", fmt.Errorf("JWT has no user ID")
-	}
-
-	switch header.mode {
-	case ModeSession:
-		// Session mode: check user + OS username mapping.
-		if _, err := s.authorizer.Authorize(userAuth.UserId, header.username); err != nil {
-			return "", fmt.Errorf("authorize session for %s: %w", header.username, err)
-		}
-	default:
-		// Attach mode: just check user is in the authorized list (wildcard OS user).
-		if _, err := s.authorizer.Authorize(userAuth.UserId, "*"); err != nil {
-			return "", fmt.Errorf("user not authorized for VNC: %w", err)
-		}
-	}
-
-	return userAuth.UserId, nil
+	return userIDHash.String(), nil
 }
 
-// ensureJWTValidator lazily initializes the JWT validator. Must be called with mu held.
-func (s *Server) ensureJWTValidator() error {
-	if s.jwtValidator != nil && s.jwtExtractor != nil {
-		return nil
-	}
-	if s.jwtConfig == nil {
-		return fmt.Errorf("no JWT config")
-	}
+var vncIdentityMagic = []byte("NBV3")
 
-	// Enable IdP key refresh so JWKS rotations don't latch the validator
-	// off until daemon restart.
-	s.jwtValidator = nbjwt.NewValidator(
-		s.jwtConfig.Issuer,
-		s.jwtConfig.Audiences,
-		s.jwtConfig.KeysLocation,
-		true,
-	)
+// Noise_IK_25519_ChaChaPoly_SHA256 message sizes (with empty payloads).
+//   msg1 = e(32) + s_AEAD(32+16) + payload_AEAD(0+16) = 96 bytes
+//   msg2 = e(32) + payload_AEAD(0+16) = 48 bytes
+const (
+	noiseInitiatorMsgLen = 96
+	noiseResponderMsgLen = 48
+)
 
-	var opts []nbjwt.ClaimsExtractorOption
-	if len(s.jwtConfig.Audiences) > 0 {
-		opts = append(opts, nbjwt.WithAudience(s.jwtConfig.Audiences[0]))
-	}
-	if claim := s.authorizer.GetUserIDClaim(); claim != "" {
-		opts = append(opts, nbjwt.WithUserIDClaim(claim))
-	}
-	s.jwtExtractor = nbjwt.NewClaimsExtractor(opts...)
+// vncNoiseSuite pins the cipher suite for the VNC handshake. Changing
+// it requires bumping vncIdentityMagic so old clients fail closed.
+var vncNoiseSuite = noise.NewCipherSuite(noise.DH25519, noise.CipherChaChaPoly, noise.HashSHA256)
 
-	return nil
-}
-
-func (s *Server) checkTokenAge(token *gojwt.Token) error {
-	maxAge := defaultJWTMaxTokenAge
-	if s.jwtConfig != nil && s.jwtConfig.MaxTokenAge > 0 {
-		maxAge = int(s.jwtConfig.MaxTokenAge)
-	}
-	return nbjwt.CheckTokenAge(token, time.Duration(maxAge)*time.Second)
-}
-
-// readConnectionHeader reads the NetBird VNC session header from the connection.
-// Format: [mode: 1 byte] [username_len: 2 bytes BE] [username: N bytes]
+// readConnectionHeader reads the NetBird VNC session header. Format:
 //
-//	[jwt_len: 2 bytes BE] [jwt: N bytes]
+//	[mode: 1] [username_len: 2 BE] [username: N]
+//	[opt magic "NBV3": 4] [noise_msg1: 96]
+//	  (server writes [noise_msg2: 48] here when the magic is present)
+//	[session_id: 4 BE] [width: 2 BE] [height: 2 BE]
 //
-// Uses a short timeout: our WASM proxy sends the header immediately after
-// connecting. Standard VNC clients don't send anything first (server speaks
-// first in RFB), so they time out and get the default attach mode.
-func readConnectionHeader(conn net.Conn) (*connectionHeader, error) {
+// Standard VNC clients don't speak first, so they time out on the first
+// read and fall through to attach mode (which auth still rejects when
+// no Noise handshake completed).
+func (s *Server) readConnectionHeader(conn net.Conn) (*connectionHeader, error) {
 	if err := conn.SetReadDeadline(time.Now().Add(2 * time.Second)); err != nil {
 		return nil, fmt.Errorf("set deadline: %w", err)
 	}
@@ -764,11 +814,9 @@ func readConnectionHeader(conn net.Conn) (*connectionHeader, error) {
 
 	var hdr [3]byte
 	if _, err := io.ReadFull(conn, hdr[:]); err != nil {
-		// Timeout or error: assume no header, use attach mode.
 		return &connectionHeader{mode: ModeAttach}, nil
 	}
 
-	// Restore a longer deadline for reading variable-length fields.
 	if err := conn.SetReadDeadline(time.Now().Add(5 * time.Second)); err != nil {
 		return nil, fmt.Errorf("set deadline: %w", err)
 	}
@@ -788,48 +836,93 @@ func readConnectionHeader(conn net.Conn) (*connectionHeader, error) {
 		username = string(buf)
 	}
 
-	// Read JWT token length and data.
-	var jwtLenBuf [2]byte
-	var jwtToken string
-	if _, err := io.ReadFull(conn, jwtLenBuf[:]); err == nil {
-		jwtLen := binary.BigEndian.Uint16(jwtLenBuf[:])
-		if jwtLen >= 8192 {
-			return nil, fmt.Errorf("jwt too long: %d (max 8191)", jwtLen)
-		}
-		if jwtLen > 0 {
-			buf := make([]byte, jwtLen)
-			if _, err := io.ReadFull(conn, buf); err != nil {
-				return nil, fmt.Errorf("read JWT: %w", err)
-			}
-			jwtToken = string(buf)
-		}
+	br := bufio.NewReader(conn)
+	clientStatic, identityVerified, err := s.maybeRunNoiseHandshake(conn, br)
+	if err != nil {
+		return nil, err
 	}
 
-	// Read optional Windows session ID (4 bytes BE). Missing = 0 (console/auto).
 	var sessionID uint32
 	var sidBuf [4]byte
-	if _, err := io.ReadFull(conn, sidBuf[:]); err == nil {
+	if _, err := io.ReadFull(br, sidBuf[:]); err == nil {
 		sessionID = binary.BigEndian.Uint32(sidBuf[:])
 	}
 
-	// Read optional requested viewport size (2x uint16 BE). Missing = 0 (default).
 	var width, height uint16
 	var geomBuf [4]byte
-	if _, err := io.ReadFull(conn, geomBuf[:]); err == nil {
+	if _, err := io.ReadFull(br, geomBuf[:]); err == nil {
 		width = binary.BigEndian.Uint16(geomBuf[0:2])
 		height = binary.BigEndian.Uint16(geomBuf[2:4])
 	}
 
 	return &connectionHeader{
-		mode:      mode,
-		username:  username,
-		jwt:       jwtToken,
-		sessionID: sessionID,
-		width:     width,
-		height:    height,
+		mode:             mode,
+		username:         username,
+		clientStatic:     clientStatic,
+		sessionID:        sessionID,
+		width:            width,
+		height:           height,
+		identityVerified: identityVerified,
 	}, nil
 }
 
+// maybeRunNoiseHandshake performs the responder side of a Noise_IK
+// handshake when the client sends the v3 magic. Returns the client static
+// public key learned from the handshake. Any handshake failure is fatal
+// (fail closed).
+func (s *Server) maybeRunNoiseHandshake(conn net.Conn, br *bufio.Reader) ([]byte, bool, error) {
+	peek, err := br.Peek(len(vncIdentityMagic))
+	if err != nil || !bytes.Equal(peek, vncIdentityMagic) {
+		return nil, false, nil
+	}
+	if _, err := br.Discard(len(vncIdentityMagic)); err != nil {
+		return nil, false, fmt.Errorf("discard identity magic: %w", err)
+	}
+
+	msg1 := make([]byte, noiseInitiatorMsgLen)
+	if _, err := io.ReadFull(br, msg1); err != nil {
+		return nil, false, fmt.Errorf("read noise msg1: %w", err)
+	}
+
+	// Agents on loopback authenticate via the agent token, not this
+	// handshake. Consume the replayed bytes and skip the response.
+	if s.disableAuth {
+		return nil, true, nil
+	}
+
+	if len(s.identityKey) != 32 || len(s.identityPublic) != 32 {
+		return nil, false, errors.New("identity key not configured")
+	}
+	state, err := noise.NewHandshakeState(noise.Config{
+		CipherSuite:   vncNoiseSuite,
+		Pattern:       noise.HandshakeIK,
+		Initiator:     false,
+		StaticKeypair: noise.DHKey{Private: s.identityKey, Public: s.identityPublic},
+	})
+	if err != nil {
+		return nil, false, fmt.Errorf("noise responder init: %w", err)
+	}
+	if _, _, _, err := state.ReadMessage(nil, msg1); err != nil {
+		return nil, false, fmt.Errorf("noise read msg1: %w", err)
+	}
+	msg2, _, _, err := state.WriteMessage(nil, nil)
+	if err != nil {
+		return nil, false, fmt.Errorf("noise write msg2: %w", err)
+	}
+	if len(msg2) != noiseResponderMsgLen {
+		return nil, false, fmt.Errorf("noise responder produced %d bytes, expected %d", len(msg2), noiseResponderMsgLen)
+	}
+	if _, err := conn.Write(msg2); err != nil {
+		return nil, false, fmt.Errorf("write noise msg2: %w", err)
+	}
+
+	clientStatic := state.PeerStatic()
+	if len(clientStatic) != 32 {
+		return nil, false, errors.New("noise peer static missing")
+	}
+	return clientStatic, true, nil
+}
+
 // verifyAgentToken validates the agent token prefix when configured. Returns
 // false when the token is invalid or unreadable; the connection is closed.
 func (s *Server) verifyAgentToken(conn net.Conn, connLog *log.Entry) bool {
@@ -865,25 +958,34 @@ func (s *Server) verifyAgentToken(conn net.Conn, connLog *log.Entry) bool {
 	return true
 }
 
-// authorizeJWT performs JWT validation when auth is enabled. Returns the
-// enriched log entry, jwt user ID (empty when auth disabled), and ok=false
-// if the connection was rejected.
-func (s *Server) authorizeJWT(conn net.Conn, header *connectionHeader, connLog *log.Entry) (*log.Entry, string, bool) {
+// authorizeSession runs the Noise_IK handshake when auth is enabled.
+// Returns the enriched log entry, user identity hash (empty when auth
+// disabled), and ok=false if the connection was rejected.
+func (s *Server) authorizeSession(conn net.Conn, header *connectionHeader, connLog *log.Entry) (*log.Entry, string, bool) {
 	if s.disableAuth {
 		return connLog, "", true
 	}
-	if s.jwtConfig == nil {
-		rejectConnection(conn, codeMessage(RejectCodeAuthConfig, "auth enabled but no identity provider configured"))
-		connLog.Warn("auth rejected: no identity provider configured")
-		return connLog, "", false
-	}
-	jwtUserID, err := s.authenticateJWT(header)
+	userID, err := s.authenticateSession(header)
 	if err != nil {
-		rejectConnection(conn, codeMessage(jwtErrorCode(err), err.Error()))
+		rejectConnection(conn, codeMessage(RejectCodeAuthForbidden, err.Error()))
 		connLog.Warnf("auth rejected: %v", err)
 		return connLog, "", false
 	}
-	return connLog.WithField("jwt_user", jwtUserID), jwtUserID, true
+	return connLog.WithFields(log.Fields{
+		"session_user": userID,
+		"session_key":  sessionKeyFingerprint(header.clientStatic),
+	}), userID, true
+}
+
+// sessionKeyFingerprint returns a short hex fingerprint of a client
+// static key for log correlation. Distinct VNC sessions of the same
+// user end up with distinct fingerprints because each session mints a
+// fresh keypair, so this lets an operator tell parallel sessions apart.
+func sessionKeyFingerprint(clientStatic []byte) string {
+	if len(clientStatic) < 4 {
+		return ""
+	}
+	return hex.EncodeToString(clientStatic[:4])
 }
 
 // acquireSessionResources returns the capturer/injector to use for this