Add daemon into newt

authdaemon.go

@@ -0,0 +1,151 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"runtime"
+
+	"github.com/fosrl/newt/authdaemon"
+	"github.com/fosrl/newt/logger"
+)
+
+const (
+	defaultPrincipalsPath = "/var/run/auth-daemon/principals"
+	defaultCACertPath     = "/etc/ssh/ca.pem"
+)
+
+var (
+	errPresharedKeyRequired = errors.New("auth-daemon-key is required when --auth-daemon is enabled")
+	errRootRequired         = errors.New("auth-daemon must be run as root (use sudo)")
+	authDaemonServer        *authdaemon.Server // Global auth daemon server instance
+)
+
+// startAuthDaemon initializes and starts the auth daemon in the background.
+// It validates requirements (Linux, root, preshared key) and starts the server
+// in a goroutine so it runs alongside normal newt operation.
+func startAuthDaemon(ctx context.Context) error {
+	// Validation
+	if runtime.GOOS != "linux" {
+		return fmt.Errorf("auth-daemon is only supported on Linux, not %s", runtime.GOOS)
+	}
+	if os.Geteuid() != 0 {
+		return errRootRequired
+	}
+
+	// Use defaults if not set
+	principalsFile := authDaemonPrincipalsFile
+	if principalsFile == "" {
+		principalsFile = defaultPrincipalsPath
+	}
+	caCertPath := authDaemonCACertPath
+	if caCertPath == "" {
+		caCertPath = defaultCACertPath
+	}
+
+	// Create auth daemon server
+	cfg := authdaemon.Config{
+		DisableHTTPS:       true, // We run without HTTP server in newt
+		PresharedKey:       "this-key-is-not-used",   // Not used in embedded mode, but set to non-empty to satisfy validation
+		PrincipalsFilePath: principalsFile,
+		CACertPath:         caCertPath,
+		Force:              true,
+	}
+
+	srv, err := authdaemon.NewServer(cfg)
+	if err != nil {
+		return fmt.Errorf("create auth daemon server: %w", err)
+	}
+
+	authDaemonServer = srv
+
+	// Start the auth daemon in a goroutine so it runs alongside newt
+	go func() {
+		logger.Info("Auth daemon starting (native mode, no HTTP server)")
+		if err := srv.Run(ctx); err != nil {
+			logger.Error("Auth daemon error: %v", err)
+		}
+		logger.Info("Auth daemon stopped")
+	}()
+
+	return nil
+}
+
+
+
+// runPrincipalsCmd executes the principals subcommand logic
+func runPrincipalsCmd(args []string) {
+	opts := struct {
+		PrincipalsFile string
+		Username       string
+	}{
+		PrincipalsFile: defaultPrincipalsPath,
+	}
+
+	// Parse flags manually
+	for i := 0; i < len(args); i++ {
+		switch args[i] {
+		case "--principals-file":
+			if i+1 >= len(args) {
+				fmt.Fprintf(os.Stderr, "Error: --principals-file requires a value\n")
+				os.Exit(1)
+			}
+			opts.PrincipalsFile = args[i+1]
+			i++
+		case "--username":
+			if i+1 >= len(args) {
+				fmt.Fprintf(os.Stderr, "Error: --username requires a value\n")
+				os.Exit(1)
+			}
+			opts.Username = args[i+1]
+			i++
+		case "--help", "-h":
+			printPrincipalsHelp()
+			os.Exit(0)
+		default:
+			fmt.Fprintf(os.Stderr, "Error: unknown flag: %s\n", args[i])
+			printPrincipalsHelp()
+			os.Exit(1)
+		}
+	}
+
+	// Validation
+	if opts.Username == "" {
+		fmt.Fprintf(os.Stderr, "Error: username is required\n")
+		printPrincipalsHelp()
+		os.Exit(1)
+	}
+
+	// Get principals
+	list, err := authdaemon.GetPrincipals(opts.PrincipalsFile, opts.Username)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
+	if len(list) == 0 {
+		fmt.Println("")
+		return
+	}
+	for _, principal := range list {
+		fmt.Println(principal)
+	}
+}
+
+func printPrincipalsHelp() {
+	fmt.Fprintf(os.Stderr, `Usage: newt principals [flags]
+
+Output principals for a username (for AuthorizedPrincipalsCommand in sshd_config).
+Read the principals file and print principals that match the given username, one per line.
+Configure in sshd_config with AuthorizedPrincipalsCommand and %%u for the username.
+
+Flags:
+  --principals-file string   Path to the principals file (default "%s")
+  --username string          Username to look up (required)
+  --help, -h                 Show this help message
+
+Example:
+  newt principals --username alice
+
+`, defaultPrincipalsPath)
+}

authdaemon/connection.go

@@ -0,0 +1,27 @@
+package authdaemon
+
+import (
+	"github.com/fosrl/newt/logger"
+)
+
+// ProcessConnection runs the same logic as POST /connection: CA cert, user create/reconcile, principals.
+// Use this when DisableHTTPS is true (e.g. embedded in Newt) instead of calling the API.
+func (s *Server) ProcessConnection(req ConnectionRequest) {
+	logger.Info("connection: niceId=%q username=%q metadata.sudo=%v metadata.homedir=%v",
+		req.NiceId, req.Username, req.Metadata.Sudo, req.Metadata.Homedir)
+
+	cfg := &s.cfg
+	if cfg.CACertPath != "" {
+		if err := writeCACertIfNotExists(cfg.CACertPath, req.CaCert, cfg.Force); err != nil {
+			logger.Warn("auth-daemon: write CA cert: %v", err)
+		}
+	}
+	if err := ensureUser(req.Username, req.Metadata); err != nil {
+		logger.Warn("auth-daemon: ensure user: %v", err)
+	}
+	if cfg.PrincipalsFilePath != "" {
+		if err := writePrincipals(cfg.PrincipalsFilePath, req.Username, req.NiceId); err != nil {
+			logger.Warn("auth-daemon: write principals: %v", err)
+		}
+	}
+}

authdaemon/host_linux.go

@@ -0,0 +1,224 @@
+//go:build linux
+
+package authdaemon
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"os/user"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/fosrl/newt/logger"
+)
+
+// writeCACertIfNotExists writes contents to path. If the file already exists: when force is false, skip; when force is true, overwrite only if content differs.
+func writeCACertIfNotExists(path, contents string, force bool) error {
+	contents = strings.TrimSpace(contents)
+	if contents != "" && !strings.HasSuffix(contents, "\n") {
+		contents += "\n"
+	}
+	existing, err := os.ReadFile(path)
+	if err == nil {
+		existingStr := strings.TrimSpace(string(existing))
+		if existingStr != "" && !strings.HasSuffix(existingStr, "\n") {
+			existingStr += "\n"
+		}
+		if existingStr == contents {
+			logger.Debug("auth-daemon: CA cert unchanged at %s, skipping write", path)
+			return nil
+		}
+		if !force {
+			logger.Debug("auth-daemon: CA cert already exists at %s, skipping write (Force disabled)", path)
+			return nil
+		}
+	} else if !os.IsNotExist(err) {
+		return fmt.Errorf("read %s: %w", path, err)
+	}
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("mkdir %s: %w", dir, err)
+	}
+	if err := os.WriteFile(path, []byte(contents), 0644); err != nil {
+		return fmt.Errorf("write CA cert: %w", err)
+	}
+	logger.Info("auth-daemon: wrote CA cert to %s", path)
+	return nil
+}
+
+// writePrincipals updates the principals file at path: JSON object keyed by username, value is array of principals. Adds username and niceId to that user's list (deduped).
+func writePrincipals(path, username, niceId string) error {
+	if path == "" {
+		return nil
+	}
+	username = strings.TrimSpace(username)
+	niceId = strings.TrimSpace(niceId)
+	if username == "" {
+		return nil
+	}
+	data := make(map[string][]string)
+	if raw, err := os.ReadFile(path); err == nil {
+		_ = json.Unmarshal(raw, &data)
+	}
+	list := data[username]
+	seen := make(map[string]struct{}, len(list)+2)
+	for _, p := range list {
+		seen[p] = struct{}{}
+	}
+	for _, p := range []string{username, niceId} {
+		if p == "" {
+			continue
+		}
+		if _, ok := seen[p]; !ok {
+			seen[p] = struct{}{}
+			list = append(list, p)
+		}
+	}
+	data[username] = list
+	body, err := json.Marshal(data)
+	if err != nil {
+		return fmt.Errorf("marshal principals: %w", err)
+	}
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("mkdir %s: %w", dir, err)
+	}
+	if err := os.WriteFile(path, body, 0644); err != nil {
+		return fmt.Errorf("write principals: %w", err)
+	}
+	logger.Debug("auth-daemon: wrote principals to %s", path)
+	return nil
+}
+
+// sudoGroup returns the name of the sudo group (wheel or sudo) that exists on the system. Prefers wheel.
+func sudoGroup() string {
+	f, err := os.Open("/etc/group")
+	if err != nil {
+		return "sudo"
+	}
+	defer f.Close()
+	sc := bufio.NewScanner(f)
+	hasWheel := false
+	hasSudo := false
+	for sc.Scan() {
+		line := sc.Text()
+		if strings.HasPrefix(line, "wheel:") {
+			hasWheel = true
+		}
+		if strings.HasPrefix(line, "sudo:") {
+			hasSudo = true
+		}
+	}
+	if hasWheel {
+		return "wheel"
+	}
+	if hasSudo {
+		return "sudo"
+	}
+	return "sudo"
+}
+
+// ensureUser creates the system user if missing, or reconciles sudo and homedir to match meta.
+func ensureUser(username string, meta ConnectionMetadata) error {
+	if username == "" {
+		return nil
+	}
+	u, err := user.Lookup(username)
+	if err != nil {
+		if _, ok := err.(user.UnknownUserError); !ok {
+			return fmt.Errorf("lookup user %s: %w", username, err)
+		}
+		return createUser(username, meta)
+	}
+	return reconcileUser(u, meta)
+}
+
+func createUser(username string, meta ConnectionMetadata) error {
+	args := []string{"-s", "/bin/bash"}
+	if meta.Homedir {
+		args = append(args, "-m")
+	} else {
+		args = append(args, "-M")
+	}
+	args = append(args, username)
+	cmd := exec.Command("useradd", args...)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("useradd %s: %w (output: %s)", username, err, string(out))
+	}
+	logger.Info("auth-daemon: created user %s (homedir=%v)", username, meta.Homedir)
+	if meta.Sudo {
+		group := sudoGroup()
+		cmd := exec.Command("usermod", "-aG", group, username)
+		if out, err := cmd.CombinedOutput(); err != nil {
+			logger.Warn("auth-daemon: usermod -aG %s %s: %v (output: %s)", group, username, err, string(out))
+		} else {
+			logger.Info("auth-daemon: added %s to %s", username, group)
+		}
+	}
+	return nil
+}
+
+func mustAtoi(s string) int {
+	n, _ := strconv.Atoi(s)
+	return n
+}
+
+func reconcileUser(u *user.User, meta ConnectionMetadata) error {
+	group := sudoGroup()
+	inGroup, err := userInGroup(u.Username, group)
+	if err != nil {
+		logger.Warn("auth-daemon: check group %s: %v", group, err)
+		inGroup = false
+	}
+	if meta.Sudo && !inGroup {
+		cmd := exec.Command("usermod", "-aG", group, u.Username)
+		if out, err := cmd.CombinedOutput(); err != nil {
+			logger.Warn("auth-daemon: usermod -aG %s %s: %v (output: %s)", group, u.Username, err, string(out))
+		} else {
+			logger.Info("auth-daemon: added %s to %s", u.Username, group)
+		}
+	} else if !meta.Sudo && inGroup {
+		cmd := exec.Command("gpasswd", "-d", u.Username, group)
+		if out, err := cmd.CombinedOutput(); err != nil {
+			logger.Warn("auth-daemon: gpasswd -d %s %s: %v (output: %s)", u.Username, group, err, string(out))
+		} else {
+			logger.Info("auth-daemon: removed %s from %s", u.Username, group)
+		}
+	}
+	if meta.Homedir && u.HomeDir != "" {
+		if st, err := os.Stat(u.HomeDir); err != nil || !st.IsDir() {
+			if err := os.MkdirAll(u.HomeDir, 0755); err != nil {
+				logger.Warn("auth-daemon: mkdir %s: %v", u.HomeDir, err)
+			} else {
+				uid, gid := mustAtoi(u.Uid), mustAtoi(u.Gid)
+				_ = os.Chown(u.HomeDir, uid, gid)
+				logger.Info("auth-daemon: created home %s for %s", u.HomeDir, u.Username)
+			}
+		}
+	}
+	return nil
+}
+
+func userInGroup(username, groupName string) (bool, error) {
+	// getent group wheel returns "wheel:x:10:user1,user2"
+	cmd := exec.Command("getent", "group", groupName)
+	out, err := cmd.Output()
+	if err != nil {
+		return false, err
+	}
+	parts := strings.SplitN(strings.TrimSpace(string(out)), ":", 4)
+	if len(parts) < 4 {
+		return false, nil
+	}
+	members := strings.Split(parts[3], ",")
+	for _, m := range members {
+		if strings.TrimSpace(m) == username {
+			return true, nil
+		}
+	}
+	return false, nil
+}

authdaemon/host_stub.go

@@ -0,0 +1,22 @@
+//go:build !linux
+
+package authdaemon
+
+import "fmt"
+
+var errLinuxOnly = fmt.Errorf("auth-daemon PAM agent is only supported on Linux")
+
+// writeCACertIfNotExists returns an error on non-Linux.
+func writeCACertIfNotExists(path, contents string, force bool) error {
+	return errLinuxOnly
+}
+
+// ensureUser returns an error on non-Linux.
+func ensureUser(username string, meta ConnectionMetadata) error {
+	return errLinuxOnly
+}
+
+// writePrincipals returns an error on non-Linux.
+func writePrincipals(path, username, niceId string) error {
+	return errLinuxOnly
+}

authdaemon/principals.go

@@ -0,0 +1,28 @@
+package authdaemon
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+// GetPrincipals reads the principals data file at path, looks up the given user, and returns that user's principals as a string slice.
+// The file format is JSON: object with username keys and array-of-principals values, e.g. {"alice":["alice","usr-123"],"bob":["bob","usr-456"]}.
+// If the user is not found or the file is missing, returns nil and nil.
+func GetPrincipals(path, user string) ([]string, error) {
+	if path == "" {
+		return nil, fmt.Errorf("principals file path is required")
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("read principals file: %w", err)
+	}
+	var m map[string][]string
+	if err := json.Unmarshal(data, &m); err != nil {
+		return nil, fmt.Errorf("parse principals file: %w", err)
+	}
+	return m[user], nil
+}

authdaemon/routes.go

@@ -0,0 +1,56 @@
+package authdaemon
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// registerRoutes registers all API routes. Add new endpoints here.
+func (s *Server) registerRoutes() {
+	s.mux.HandleFunc("/health", s.handleHealth)
+	s.mux.HandleFunc("/connection", s.handleConnection)
+}
+
+// ConnectionMetadata is the metadata object in POST /connection.
+type ConnectionMetadata struct {
+	Sudo    bool `json:"sudo"`
+	Homedir bool `json:"homedir"`
+}
+
+// ConnectionRequest is the JSON body for POST /connection.
+type ConnectionRequest struct {
+	CaCert   string             `json:"caCert"`
+	NiceId   string             `json:"niceId"`
+	Username string             `json:"username"`
+	Metadata ConnectionMetadata `json:"metadata"`
+}
+
+// healthResponse is the JSON body for GET /health.
+type healthResponse struct {
+	Status string `json:"status"`
+}
+
+// handleHealth responds with 200 and {"status":"ok"}.
+func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(healthResponse{Status: "ok"})
+}
+
+// handleConnection accepts POST with connection payload and delegates to ProcessConnection.
+func (s *Server) handleConnection(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	var req ConnectionRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		http.Error(w, "Bad Request", http.StatusBadRequest)
+		return
+	}
+	s.ProcessConnection(req)
+	w.WriteHeader(http.StatusOK)
+}

authdaemon/server.go

@@ -0,0 +1,179 @@
+package authdaemon
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/subtle"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"fmt"
+	"math/big"
+	"net/http"
+	"os"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/fosrl/newt/logger"
+)
+
+type Config struct {
+	// DisableHTTPS: when true, Run() does not start the HTTPS server (for embedded use inside Newt). Call ProcessConnection directly for connection events.
+	DisableHTTPS       bool
+	Port               int    // Required when DisableHTTPS is false. Listen port for the HTTPS server. No default.
+	PresharedKey       string // Required when DisableHTTPS is false. HTTP auth (Authorization: Bearer <key> or X-Preshared-Key: <key>). No default.
+	CACertPath         string // Required. Where to write the CA cert (e.g. /etc/ssh/ca.pem). No default.
+	Force              bool   // If true, overwrite existing CA cert (and other items) when content differs. Default false.
+	PrincipalsFilePath string // Required. Path to the principals data file (JSON: username -> array of principals). No default.
+}
+
+type Server struct {
+	cfg          Config
+	addr         string
+	presharedKey string
+	mux          *http.ServeMux
+	tlsCert      tls.Certificate
+}
+
+// generateTLSCert creates a self-signed certificate and key in memory (no disk).
+func generateTLSCert() (tls.Certificate, error) {
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("generate key: %w", err)
+	}
+	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("serial: %w", err)
+	}
+	tmpl := &x509.Certificate{
+		SerialNumber: serial,
+		Subject: pkix.Name{
+			CommonName: "localhost",
+		},
+		NotBefore:             time.Now(),
+		NotAfter:              time.Now().Add(365 * 24 * time.Hour),
+		KeyUsage:              x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		BasicConstraintsValid: true,
+		DNSNames:              []string{"localhost", "127.0.0.1"},
+	}
+	certDER, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, key.Public(), key)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("create certificate: %w", err)
+	}
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("marshal key: %w", err)
+	}
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
+	cert, err := tls.X509KeyPair(certPEM, keyPEM)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("x509 key pair: %w", err)
+	}
+	return cert, nil
+}
+
+// authMiddleware wraps next and requires a valid preshared key on every request.
+// Accepts Authorization: Bearer <key> or X-Preshared-Key: <key>.
+func (s *Server) authMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		key := ""
+		if v := r.Header.Get("Authorization"); strings.HasPrefix(v, "Bearer ") {
+			key = strings.TrimSpace(strings.TrimPrefix(v, "Bearer "))
+		}
+		if key == "" {
+			key = strings.TrimSpace(r.Header.Get("X-Preshared-Key"))
+		}
+		if key == "" || subtle.ConstantTimeCompare([]byte(key), []byte(s.presharedKey)) != 1 {
+			http.Error(w, "Unauthorized", http.StatusUnauthorized)
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+// NewServer builds a new auth-daemon server from cfg. Port, PresharedKey, CACertPath, and PrincipalsFilePath are required (no defaults).
+func NewServer(cfg Config) (*Server, error) {
+	if runtime.GOOS != "linux" {
+		return nil, fmt.Errorf("auth-daemon is only supported on Linux, not %s", runtime.GOOS)
+	}
+	if !cfg.DisableHTTPS {
+		if cfg.Port <= 0 {
+			return nil, fmt.Errorf("port is required and must be positive")
+		}
+		if cfg.PresharedKey == "" {
+			return nil, fmt.Errorf("preshared key is required")
+		}
+	}
+	if cfg.CACertPath == "" {
+		return nil, fmt.Errorf("CACertPath is required")
+	}
+	if cfg.PrincipalsFilePath == "" {
+		return nil, fmt.Errorf("PrincipalsFilePath is required")
+	}
+	s := &Server{cfg: cfg}
+	if !cfg.DisableHTTPS {
+		cert, err := generateTLSCert()
+		if err != nil {
+			return nil, err
+		}
+		s.addr = fmt.Sprintf(":%d", cfg.Port)
+		s.presharedKey = cfg.PresharedKey
+		s.mux = http.NewServeMux()
+		s.tlsCert = cert
+		s.registerRoutes()
+	}
+	return s, nil
+}
+
+// Run starts the HTTPS server (unless DisableHTTPS) and blocks until ctx is cancelled or the server errors.
+// When DisableHTTPS is true, Run() blocks on ctx only and does not listen; use ProcessConnection for connection events.
+func (s *Server) Run(ctx context.Context) error {
+	if s.cfg.DisableHTTPS {
+		logger.Info("auth-daemon running (HTTPS disabled)")
+		<-ctx.Done()
+		s.cleanupPrincipalsFile()
+		return nil
+	}
+	tcfg := &tls.Config{
+		Certificates: []tls.Certificate{s.tlsCert},
+		MinVersion:   tls.VersionTLS12,
+	}
+	handler := s.authMiddleware(s.mux)
+	srv := &http.Server{
+		Addr:              s.addr,
+		Handler:           handler,
+		TLSConfig:         tcfg,
+		ReadTimeout:       10 * time.Second,
+		WriteTimeout:      10 * time.Second,
+		ReadHeaderTimeout: 5 * time.Second,
+		IdleTimeout:       60 * time.Second,
+	}
+	go func() {
+		<-ctx.Done()
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+		if err := srv.Shutdown(shutdownCtx); err != nil {
+			logger.Warn("auth-daemon shutdown: %v", err)
+		}
+	}()
+	logger.Info("auth-daemon listening on https://127.0.0.1%s", s.addr)
+	if err := srv.ListenAndServeTLS("", ""); err != nil && err != http.ErrServerClosed {
+		return err
+	}
+	s.cleanupPrincipalsFile()
+	return nil
+}
+
+func (s *Server) cleanupPrincipalsFile() {
+	if s.cfg.PrincipalsFilePath != "" {
+		if err := os.Remove(s.cfg.PrincipalsFilePath); err != nil && !os.IsNotExist(err) {
+			logger.Warn("auth-daemon: remove principals file: %v", err)
+		}
+	}
+}

main.go

@@ -1,7 +1,9 @@
 package main
 
 import (
+	"bytes"
 	"context"
+	"crypto/tls"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -11,12 +13,12 @@ import (
 	"net/netip"
 	"os"
 	"os/signal"
-	"path/filepath"
 	"strconv"
 	"strings"
 	"syscall"
 	"time"
 
+	"github.com/fosrl/newt/authdaemon"
 	"github.com/fosrl/newt/docker"
 	"github.com/fosrl/newt/healthcheck"
 	"github.com/fosrl/newt/logger"
@@ -58,10 +60,6 @@ type ExitNodeData struct {
 	ExitNodes []ExitNode `json:"exitNodes"`
 }
 
-type SSHPublicKeyData struct {
-	PublicKey string `json:"publicKey"`
-}
-
 // ExitNode represents an exit node with an ID, endpoint, and weight.
 type ExitNode struct {
 	ID                     int     `json:"exitNodeId"`
@@ -134,6 +132,10 @@ var (
 	preferEndpoint                     string
 	healthMonitor                      *healthcheck.Monitor
 	enforceHealthcheckCert             bool
+	authDaemonKey                      string
+	authDaemonPrincipalsFile           string
+	authDaemonCACertPath               string
+	authDaemonEnabled                  bool
 	// Build/version (can be overridden via -ldflags "-X main.newtVersion=...")
 	newtVersion = "version_replaceme"
 
@@ -156,6 +158,28 @@ var (
 )
 
 func main() {
+	// Check for subcommands first (only principals exits early)
+	if len(os.Args) > 1 {
+		switch os.Args[1] {
+		case "auth-daemon":
+			// Run principals subcommand only if the next argument is "principals"
+			if len(os.Args) > 2 && os.Args[2] == "principals" {
+				runPrincipalsCmd(os.Args[3:])
+				return
+			}
+
+			// auth-daemon subcommand without "principals" - show help
+			fmt.Println("Error: auth-daemon subcommand requires 'principals' argument")
+			fmt.Println()
+			fmt.Println("Usage:")
+			fmt.Println("  newt auth-daemon principals [options]")
+			fmt.Println()
+
+			// If not "principals", exit the switch to continue with normal execution
+			return
+		}
+	}
+
 	// Check if we're running as a Windows service
 	if isWindowsService() {
 		runService("NewtWireguardService", false, os.Args[1:])
@@ -187,6 +211,10 @@ func runNewtMain(ctx context.Context) {
 	updownScript = os.Getenv("UPDOWN_SCRIPT")
 	interfaceName = os.Getenv("INTERFACE")
 	portStr := os.Getenv("PORT")
+	authDaemonKey = os.Getenv("AD_KEY")
+	authDaemonPrincipalsFile = os.Getenv("AD_PRINCIPALS_FILE")
+	authDaemonCACertPath = os.Getenv("AD_CA_CERT_PATH")
+	authDaemonEnabledEnv := os.Getenv("AUTH_DAEMON_ENABLED")
 
 	// Metrics/observability env mirrors
 	metricsEnabledEnv := os.Getenv("NEWT_METRICS_PROMETHEUS_ENABLED")
@@ -279,10 +307,6 @@ func runNewtMain(ctx context.Context) {
 	// load the prefer endpoint just as a flag
 	flag.StringVar(&preferEndpoint, "prefer-endpoint", "", "Prefer this endpoint for the connection (if set, will override the endpoint from the server)")
 
-	// if authorizedKeysFile == "" {
-	// 	flag.StringVar(&authorizedKeysFile, "authorized-keys-file", "~/.ssh/authorized_keys", "Path to authorized keys file (if unset, no keys will be authorized)")
-	// }
-
 	// Add new mTLS flags
 	if tlsClientCert == "" {
 		flag.StringVar(&tlsClientCert, "tls-client-cert-file", "", "Path to client certificate file (PEM/DER format)")
@@ -379,6 +403,24 @@ func runNewtMain(ctx context.Context) {
 		region = regionEnv
 	}
 
+	// Auth daemon flags
+	if authDaemonKey == "" {
+		flag.StringVar(&authDaemonKey, "ad-preshared-key", "", "Preshared key for auth daemon authentication (required when --auth-daemon is true)")
+	}
+	if authDaemonPrincipalsFile == "" {
+		flag.StringVar(&authDaemonPrincipalsFile, "ad-principals-file", "/var/run/auth-daemon/principals", "Path to the principals file for auth daemon")
+	}
+	if authDaemonCACertPath == "" {
+		flag.StringVar(&authDaemonCACertPath, "ad-ca-cert-path", "/etc/ssh/ca.pem", "Path to the CA certificate file for auth daemon")
+	}
+	if authDaemonEnabledEnv == "" {
+		flag.BoolVar(&authDaemonEnabled, "auth-daemon", false, "Enable auth daemon mode (runs alongside normal newt operation)")
+	} else {
+		if v, err := strconv.ParseBool(authDaemonEnabledEnv); err == nil {
+			authDaemonEnabled = v
+		}
+	}
+
 	// do a --version check
 	version := flag.Bool("version", false, "Print the version")
 
@@ -398,6 +440,13 @@ func runNewtMain(ctx context.Context) {
 
 	logger.Init(nil)
 	loggerLevel := util.ParseLogLevel(logLevel)
+
+	// Start auth daemon if enabled
+	if authDaemonEnabled {
+		if err := startAuthDaemon(ctx); err != nil {
+			logger.Fatal("Failed to start auth daemon: %v", err)
+		}
+	}
 	logger.GetLogger().SetLevel(loggerLevel)
 
 	// Initialize telemetry after flags are parsed (so flags override env)
@@ -694,8 +743,8 @@ func runNewtMain(ctx context.Context) {
 
 		relayPort := wgData.RelayPort
 		if relayPort == 0 {
-            relayPort = 21820
-        }
+			relayPort = 21820
+		}
 
 		clientsHandleNewtConnection(wgData.PublicKey, endpoint, relayPort)
 
@@ -1168,94 +1217,6 @@ persistent_keepalive_interval=5`, util.FixKey(privateKey.String()), util.FixKey(
 		}
 	})
 
-	// EXPERIMENTAL: WHAT SHOULD WE DO ABOUT SECURITY?
-	client.RegisterHandler("newt/send/ssh/publicKey", func(msg websocket.WSMessage) {
-		logger.Debug("Received SSH public key request")
-
-		var sshPublicKeyData SSHPublicKeyData
-
-		jsonData, err := json.Marshal(msg.Data)
-		if err != nil {
-			logger.Info(fmtErrMarshaling, err)
-			return
-		}
-		if err := json.Unmarshal(jsonData, &sshPublicKeyData); err != nil {
-			logger.Info("Error unmarshaling SSH public key data: %v", err)
-			return
-		}
-
-		sshPublicKey := sshPublicKeyData.PublicKey
-
-		if authorizedKeysFile == "" {
-			logger.Debug("No authorized keys file set, skipping public key response")
-			return
-		}
-
-		// Expand tilde to home directory if present
-		expandedPath := authorizedKeysFile
-		if strings.HasPrefix(authorizedKeysFile, "~/") {
-			homeDir, err := os.UserHomeDir()
-			if err != nil {
-				logger.Error("Failed to get user home directory: %v", err)
-				return
-			}
-			expandedPath = filepath.Join(homeDir, authorizedKeysFile[2:])
-		}
-
-		// if it is set but the file does not exist, create it
-		if _, err := os.Stat(expandedPath); os.IsNotExist(err) {
-			logger.Debug("Authorized keys file does not exist, creating it: %s", expandedPath)
-			if err := os.MkdirAll(filepath.Dir(expandedPath), 0755); err != nil {
-				logger.Error("Failed to create directory for authorized keys file: %v", err)
-				return
-			}
-			if _, err := os.Create(expandedPath); err != nil {
-				logger.Error("Failed to create authorized keys file: %v", err)
-				return
-			}
-		}
-
-		// Check if the public key already exists in the file
-		fileContent, err := os.ReadFile(expandedPath)
-		if err != nil {
-			logger.Error("Failed to read authorized keys file: %v", err)
-			return
-		}
-
-		// Check if the key already exists (trim whitespace for comparison)
-		existingKeys := strings.Split(string(fileContent), "\n")
-		keyAlreadyExists := false
-		trimmedNewKey := strings.TrimSpace(sshPublicKey)
-
-		for _, existingKey := range existingKeys {
-			if strings.TrimSpace(existingKey) == trimmedNewKey && trimmedNewKey != "" {
-				keyAlreadyExists = true
-				break
-			}
-		}
-
-		if keyAlreadyExists {
-			logger.Info("SSH public key already exists in authorized keys file, skipping")
-			return
-		}
-
-		// append the public key to the authorized keys file
-		logger.Debug("Appending public key to authorized keys file: %s", sshPublicKey)
-		file, err := os.OpenFile(expandedPath, os.O_APPEND|os.O_WRONLY, 0644)
-		if err != nil {
-			logger.Error("Failed to open authorized keys file: %v", err)
-			return
-		}
-		defer file.Close()
-
-		if _, err := file.WriteString(sshPublicKey + "\n"); err != nil {
-			logger.Error("Failed to write public key to authorized keys file: %v", err)
-			return
-		}
-
-		logger.Info("SSH public key appended to authorized keys file")
-	})
-
 	// Register handler for adding health check targets
 	client.RegisterHandler("newt/healthcheck/add", func(msg websocket.WSMessage) {
 		logger.Debug("Received health check add request: %+v", msg)
@@ -1411,6 +1372,168 @@ persistent_keepalive_interval=5`, util.FixKey(privateKey.String()), util.FixKey(
 		}
 	})
 
+	// Register handler for SSH certificate issued events
+	client.RegisterHandler("newt/pam/connection", func(msg websocket.WSMessage) {
+		logger.Debug("Received SSH certificate issued message")
+
+		// Define the structure of the incoming message
+		type SSHCertData struct {
+			MessageId int    `json:"messageId"`
+			AgentPort int    `json:"agentPort"`
+			AgentHost string `json:"agentHost"`
+			CACert    string `json:"caCert"`
+			Username  string `json:"username"`
+			NiceID    string `json:"niceId"`
+			Metadata  struct {
+				Sudo    bool `json:"sudo"`
+				Homedir bool `json:"homedir"`
+			} `json:"metadata"`
+		}
+
+		var certData SSHCertData
+		jsonData, err := json.Marshal(msg.Data)
+		if err != nil {
+			logger.Error("Error marshaling SSH cert data: %v", err)
+			return
+		}
+
+		// print the received data for debugging
+		logger.Debug("Received SSH cert data: %s", string(jsonData))
+
+		if err := json.Unmarshal(jsonData, &certData); err != nil {
+			logger.Error("Error unmarshaling SSH cert data: %v", err)
+			return
+		}
+
+		// Check if we're running the auth daemon internally
+		if authDaemonServer != nil {
+			// Call ProcessConnection directly when running internally
+			logger.Debug("Calling internal auth daemon ProcessConnection for user %s", certData.Username)
+
+			authDaemonServer.ProcessConnection(authdaemon.ConnectionRequest{
+				CaCert:   certData.CACert,
+				NiceId:   certData.NiceID,
+				Username: certData.Username,
+				Metadata: authdaemon.ConnectionMetadata{
+					Sudo:    certData.Metadata.Sudo,
+					Homedir: certData.Metadata.Homedir,
+				},
+			})
+
+			// Send success response back to cloud
+			err = client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+				"messageId": certData.MessageId,
+				"complete":  true,
+			})
+
+			logger.Info("Successfully processed connection via internal auth daemon for user %s", certData.Username)
+		} else {
+			// External auth daemon mode - make HTTP request
+			// Check if auth daemon key is configured
+			if authDaemonKey == "" {
+				logger.Error("Auth daemon key not configured, cannot communicate with daemon")
+				// Send failure response back to cloud
+				err := client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+					"messageId": certData.MessageId,
+					"complete":  true,
+					"error":     "auth daemon key not configured",
+				})
+				if err != nil {
+					logger.Error("Failed to send SSH cert failure response: %v", err)
+				}
+				return
+			}
+
+			// Prepare the request body for the auth daemon
+			requestBody := map[string]interface{}{
+				"caCert":   certData.CACert,
+				"niceId":   certData.NiceID,
+				"username": certData.Username,
+				"metadata": map[string]interface{}{
+					"sudo":    certData.Metadata.Sudo,
+					"homedir": certData.Metadata.Homedir,
+				},
+			}
+
+			requestJSON, err := json.Marshal(requestBody)
+			if err != nil {
+				logger.Error("Failed to marshal auth daemon request: %v", err)
+				// Send failure response
+				client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+					"messageId": certData.MessageId,
+					"complete":  true,
+					"error":     fmt.Sprintf("failed to marshal request: %v", err),
+				})
+				return
+			}
+
+			// Create HTTPS client that skips certificate verification
+			// (auth daemon uses self-signed cert)
+			httpClient := &http.Client{
+				Transport: &http.Transport{
+					TLSClientConfig: &tls.Config{
+						InsecureSkipVerify: true,
+					},
+				},
+				Timeout: 10 * time.Second,
+			}
+
+			// Make the request to the auth daemon
+			url := fmt.Sprintf("https://%s:%d/connection", certData.AgentHost, certData.AgentPort)
+			req, err := http.NewRequest("POST", url, bytes.NewBuffer(requestJSON))
+			if err != nil {
+				logger.Error("Failed to create auth daemon request: %v", err)
+				client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+					"messageId": certData.MessageId,
+					"complete":  true,
+					"error":     fmt.Sprintf("failed to create request: %v", err),
+				})
+				return
+			}
+
+			// Set headers
+			req.Header.Set("Content-Type", "application/json")
+			req.Header.Set("Authorization", "Bearer "+authDaemonKey)
+
+			logger.Debug("Sending SSH cert to auth daemon at %s", url)
+
+			// Send the request
+			resp, err := httpClient.Do(req)
+			if err != nil {
+				logger.Error("Failed to connect to auth daemon: %v", err)
+				client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+					"messageId": certData.MessageId,
+					"complete":  true,
+					"error":     fmt.Sprintf("failed to connect to auth daemon: %v", err),
+				})
+				return
+			}
+			defer resp.Body.Close()
+
+			// Check response status
+			if resp.StatusCode != http.StatusOK {
+				logger.Error("Auth daemon returned non-OK status: %d", resp.StatusCode)
+				client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+					"messageId": certData.MessageId,
+					"complete":  true,
+					"error":     fmt.Sprintf("auth daemon returned status %d", resp.StatusCode),
+				})
+				return
+			}
+
+			logger.Info("Successfully registered SSH certificate with external auth daemon for user %s", certData.Username)
+		}
+
+		// Send success response back to cloud
+		err = client.SendMessage("ws/round-trip/complete", map[string]interface{}{
+			"messageId": certData.MessageId,
+			"complete":  true,
+		})
+		if err != nil {
+			logger.Error("Failed to send SSH cert success response: %v", err)
+		}
+	})
+
 	client.OnConnect(func() error {
 		publicKey = privateKey.PublicKey()
 		logger.Debug("Public key: %s", publicKey)