diskless-workstation/serving/enrol-broker/admin.go

// admin.go — the mTLS admin plane: the pending-queue + approve/deny JSON API.
//
// This listener is the AUTHENTICATED half of the broker and must live on the
// management network / loopback only — NEVER the boot LAN (docs invariant: the
// management plane is recon-valuable). Admins authenticate with a client cert
// issued by the fleet CA; the cert CN is recorded as who approved each enrolment.
// The fingerprint shown here is what the admin cross-checks against the device's
// Plymouth splash before approving (the human OOB gate).
package main

import (
	"crypto/tls"
	"crypto/x509"
	"log"
	"net/http"
	"os"
	"strings"
	"time"
)

func (b *broker) serveAdmin() {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /", b.handleAdminRoot)
	mux.HandleFunc("GET /pending", b.handleAdminPending)
	mux.HandleFunc("POST /approve/{id}", b.handleApprove)
	mux.HandleFunc("POST /deny/{id}", b.handleDeny)

	srv := &http.Server{
		Addr:              b.cfg.adminAddr,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      40 * time.Second, // approve blocks on step-ca
		IdleTimeout:       60 * time.Second,
	}

	if b.cfg.adminInsecure {
		log.Printf("WARNING: BROKER_ADMIN_INSECURE=true — admin UI is PLAINTEXT with NO client-cert auth. DEV ONLY. Bind to loopback and never expose it.")
		log.Fatalf("admin listener: %v", srv.ListenAndServe())
		return
	}

	if b.cfg.adminCert == "" || b.cfg.adminKey == "" || b.cfg.adminClientCA == "" {
		log.Fatalf("admin mTLS requires BROKER_ADMIN_CERT, BROKER_ADMIN_KEY and BROKER_ADMIN_CLIENT_CA (or set BROKER_ADMIN_INSECURE=true for dev)")
	}
	cert, err := tls.LoadX509KeyPair(b.cfg.adminCert, b.cfg.adminKey)
	if err != nil {
		log.Fatalf("admin server cert: %v", err)
	}
	caPEM, err := os.ReadFile(b.cfg.adminClientCA)
	if err != nil {
		log.Fatalf("admin client CA: %v", err)
	}
	pool := x509.NewCertPool()
	if !pool.AppendCertsFromPEM(caPEM) {
		log.Fatalf("admin client CA %s contains no certificates", b.cfg.adminClientCA)
	}
	srv.TLSConfig = &tls.Config{
		Certificates: []tls.Certificate{cert},
		ClientAuth:   tls.RequireAndVerifyClientCert,
		ClientCAs:    pool,
		MinVersion:   tls.VersionTLS12,
	}
	log.Fatalf("admin listener: %v", srv.ListenAndServeTLS("", ""))
}

func adminCN(r *http.Request) string {
	if r.TLS != nil && len(r.TLS.PeerCertificates) > 0 {
		if cn := r.TLS.PeerCertificates[0].Subject.CommonName; cn != "" {
			return cn
		}
		return "unknown-admin"
	}
	return "dev-insecure"
}

func (b *broker) handleAdminPending(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, b.store.Pending())
}

func (b *broker) handleApprove(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	admin := adminCN(r)
	csrPEM, ok := b.store.csrFor(id)
	if !ok {
		http.Error(w, "enrol-id not pending (expired/decided/unknown)", http.StatusConflict)
		return
	}
	csr, err := parseCSR(csrPEM)
	if err != nil {
		http.Error(w, "stored CSR unparsable: "+err.Error(), http.StatusInternalServerError)
		return
	}
	ctx, cancel := ctxWithTimeout(35 * time.Second)
	defer cancel()
	certPEM, serial, err := b.signer.Sign(ctx, csrPEM, csr.Subject.CommonName)
	if err != nil {
		log.Printf("audit approve-FAILED id=%s admin=%q err=%v", id, admin, err)
		http.Error(w, "signing failed: "+err.Error(), http.StatusBadGateway)
		return
	}
	e, err := b.store.Approve(id, certPEM, serial, admin)
	if err != nil {
		http.Error(w, err.Error(), http.StatusConflict)
		return
	}
	log.Printf("audit APPROVE id=%s cn=%q serial=%s hostnqn=%s admin=%q", e.ID, e.CN, e.CertSerial, e.Hostnqn, admin)
	respondDecision(w, r, e)
}

func (b *broker) handleDeny(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	admin := adminCN(r)
	e, err := b.store.Deny(id, admin)
	if err != nil {
		http.Error(w, err.Error(), http.StatusConflict)
		return
	}
	log.Printf("audit DENY id=%s cn=%q admin=%q", e.ID, e.CN, admin)
	respondDecision(w, r, e)
}

// respondDecision replies to an approve/deny. A caller that asks for JSON
// (Accept: application/json — the fleet-manager driving the broker as its
// authorise plane) gets the decided Enrolment (cert_serial, hostnqn, context,
// fingerprint — NOT the cert PEM, which is unexported and only reaches the
// requesting host); any other API caller keeps the original 204 (so
// verify-serving.sh and existing scripts are unaffected).
func respondDecision(w http.ResponseWriter, r *http.Request, e *Enrolment) {
	if wantsJSON(r) {
		writeJSON(w, http.StatusOK, e)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

func wantsJSON(r *http.Request) bool {
	return strings.Contains(r.Header.Get("Accept"), "application/json")
}

// handleAdminRoot: the human approval UI has moved to the fleet-manager SPA
// (WebAuthn-passkey gated), which drives this plane's JSON API over mTLS. This
// listener is now API-only — the old embedded HTML console was retired to avoid a
// second, weaker (client-cert-only) human approve path parallel to the passkey
// UI. Kept as a plaintext pointer so a bookmark to the old console isn't a 404.
func (b *broker) handleAdminRoot(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	_, _ = w.Write([]byte("enrol-broker admin plane — API only.\n" +
		"  GET  /pending\n  POST /approve/{id}\n  POST /deny/{id}\n" +
		"The human approval UI is the fleet-manager SPA (passkey-gated).\n"))
}