M2 §5: pin auth attestation into InstalledMetadata and inject AUTH_PINNED_FINGERPRINT

Fetch the auth service's key attestation over mTLS at install time and
persist the fingerprint (plus kid/issued-at) in the install record. At
start, inject AUTH_PINNED_FINGERPRINT into every non-oneoff service so
the shared authclient refuses a substituted key instead of silently
trusting it (TOFU/D3). Best-effort: installs that cannot reach the auth
service backfill the pin on the next start. Skip pinning for the auth
service itself (it is the attester).

src/lib/containers/start.go

@@ -18,6 +18,7 @@ package containers
 import (
 	"context"
 	"fmt"
+	"path/filepath"
 	"strings"
 
 	"git.dcntrlized.org/Dcntrlized/Maestro/lib/docker"
@@ -64,7 +65,7 @@ func StartContainer(ctx context.Context, item types.RegistryContainer) error {
 	// downloaded from git never declares these mounts — Maestro injects them
 	// (security theme M1 §2). Failing to provision identity is fatal: a peer
 	// without a cert cannot authenticate on the mTLS edges.
-	if err := injectServiceIdentity(project, serviceName); err != nil {
+	if err := injectServiceIdentity(ctx, project, serviceName); err != nil {
 		return err
 	}
 
@@ -108,7 +109,12 @@ func StartContainer(ctx context.Context, item types.RegistryContainer) error {
 // cert/key, and the mTLS env vars into every non-oneoff compose service. The
 // env vars follow the shared-module contract (AUTH_CA_BUNDLE/AUTH_CLIENT_CERT/
 // AUTH_CLIENT_KEY) so consumers need no per-service config.
-func injectServiceIdentity(project *composetypes.Project, serviceName string) error {
+//
+// It also injects AUTH_PINNED_FINGERPRINT (M2 §5 TOFU): the auth signing key's
+// fingerprint recorded at install. A service that already has the pin skips the
+// fetch; one installed before this feature (or whose install could not reach
+// the auth service) backfills it here, best-effort.
+func injectServiceIdentity(ctx context.Context, project *composetypes.Project, serviceName string) error {
 	dataRoot, err := getDataRoot()
 	if err != nil {
 		return fmt.Errorf("resolve data root: %w", err)
@@ -135,6 +141,14 @@ func injectServiceIdentity(project *composetypes.Project, serviceName string) er
 		"AUTH_CLIENT_KEY":  identityMountDir + "/tls.key",
 	}
 
+	// The auth service is the attester itself — nothing to pin there. For every
+	// other peer, pin its signing key (fetch + persist once).
+	if serviceName != AuthServiceName {
+		if pinned := pinAuthFingerprint(ctx, serviceName); pinned != "" {
+			env["AUTH_PINNED_FINGERPRINT"] = pinned
+		}
+	}
+
 	for name, s := range project.Services {
 		if isOneoff(s) {
 			continue
@@ -147,6 +161,41 @@ func injectServiceIdentity(project *composetypes.Project, serviceName string) er
 	return nil
 }
 
+// pinAuthFingerprint returns the service's pinned auth fingerprint, fetching
+// and persisting it when the install record does not have one yet (M2 §5).
+// Best-effort: when the auth service is unreachable, it returns "" and the
+// next start retries.
+func pinAuthFingerprint(ctx context.Context, serviceName string) string {
+	dir, err := getContainerDataDir(serviceName)
+	if err != nil {
+		return ""
+	}
+	metadata, err := readInstalledMetadata(dir)
+	if err != nil {
+		return ""
+	}
+	if metadata.AuthFingerprint != "" {
+		return metadata.AuthFingerprint
+	}
+
+	att, err := fetchAuthAttestation(ctx)
+	if err != nil {
+		logger.Warn("Auth pin for %s: attestation fetch failed (will retry at next start): %v", serviceName, err)
+		return ""
+	}
+	if att.Fingerprint == "" {
+		return ""
+	}
+	metadata.AuthFingerprint = att.Fingerprint
+	metadata.AuthKid = att.Kid
+	metadata.AuthAttestedAt = att.IssuedAt
+	if err := writeMetadata(filepath.Join(dir, "metadata.json"), *metadata); err != nil {
+		logger.Warn("Auth pin for %s: persist failed: %v", serviceName, err)
+	}
+	logger.Info("Pinned auth fingerprint %s for %s", att.Fingerprint, serviceName)
+	return att.Fingerprint
+}
+
 // composeVolumes converts "src:dst:ro" mount strings to compose volume configs.
 func composeVolumes(mounts []string) []composetypes.ServiceVolumeConfig {
 	out := make([]composetypes.ServiceVolumeConfig, 0, len(mounts))