M2 §2: require a CA-issued client cert on the HTTP listener (mTLS)

Serve the listener over TLS with ClientAuth=RequireAndVerifyClientCert
trusting the instance CA (shared tlsutil.ServerConfig): only Maestro can
drive actions (T4), and the peer edge is encrypted. INSECURE_INTERNAL=1
(dev debug compose) keeps the listener plaintext for the RN client's
direct mode and hot reload.

docker-compose.debug.yaml

@@ -39,6 +39,9 @@ services:
     # Environment variables for the application
     environment:
       - DEV_MODE=true
+      # Security theme M2 §2: dev escape hatch — keep the listener plaintext
+      # so the RN client (direct mode) and hot reload work without certs.
+      - INSECURE_INTERNAL=1
       # Application configuration
       # - PORT=8080
       # - ENVIRONMENT=development

src/main.go

@@ -2,7 +2,10 @@ package main
 
 import (
 	"context"
+	"crypto/tls"
+	"net"
 	"net/http"
+	"os"
 	"strings"
 
 	"git.dcntrlized.org/Dcntrlized/KeepNote/db"
@@ -13,6 +16,7 @@ import (
 	"git.dcntrlized.org/Dcntrlized/KeepNote/middleware"
 	"git.dcntrlized.org/dcntrlized/dcntrlized-auth/authclient"
 	"git.dcntrlized.org/dcntrlized/dcntrlized-auth/authproxy"
+	"git.dcntrlized.org/dcntrlized/dcntrlized-auth/tlsutil"
 )
 
 func main() {
@@ -70,5 +74,36 @@ func main() {
 
 	handler := middleware.LoggingMiddleware(middleware.CorsMiddleware(mux))
 
-	http.ListenAndServe(":8080", handler)
+	// Security theme M2 §2: the service's listener requires a CA-issued client
+	// cert (Maestro's identity) so only Maestro can drive actions (T4) and the
+	// peer edge is encrypted. INSECURE_INTERNAL=1 keeps the dev fleet plaintext.
+	tlsCfg, err := tlsutil.ServerConfig()
+	if err != nil {
+		logger.Error("TLS setup failed: %v", err)
+		os.Exit(1)
+	}
+	if tlsCfg == nil {
+		logger.Info("KeepNote listening plaintext on :8080 (INSECURE_INTERNAL dev mode)")
+		if err := http.ListenAndServe(":8080", handler); err != nil {
+			logger.Error("HTTP server failed: %v", err)
+			os.Exit(1)
+		}
+		return
+	}
+
+	logger.Info("KeepNote listening on :8080 (mTLS, ClientAuth=RequireAndVerify)")
+	if err := serveTLS(":8080", tlsCfg, handler); err != nil {
+		logger.Error("HTTPS server failed: %v", err)
+		os.Exit(1)
+	}
+}
+
+// serveTLS runs an HTTPS listener with the given mTLS config.
+func serveTLS(addr string, cfg *tls.Config, handler http.Handler) error {
+	ln, err := net.Listen("tcp", addr)
+	if err != nil {
+		return err
+	}
+	tlsLn := tls.NewListener(ln, cfg)
+	return http.Serve(tlsLn, handler)
 }