Add MEK rotation, per-engine DEKs, and v2 ciphertext format (audit #6, #22)

Implement a two-level key hierarchy: the MEK now wraps per-engine DEKs
stored in a new barrier_keys table, rather than encrypting all barrier
entries directly. A v2 ciphertext format (0x02) embeds the key ID so the
barrier can resolve which DEK to use on decryption. v1 ciphertext remains
supported for backward compatibility.

Key changes:
- crypto: EncryptV2/DecryptV2/ExtractKeyID for v2 ciphertext with key IDs
- barrier: key registry (CreateKey, RotateKey, ListKeys, MigrateToV2, ReWrapKeys)
- seal: RotateMEK re-wraps DEKs without re-encrypting data
- engine: Mount auto-creates per-engine DEK
- REST + gRPC: barrier/keys, barrier/rotate-mek, barrier/rotate-key, barrier/migrate
- proto: BarrierService (v1 + v2) with ListKeys, RotateMEK, RotateKey, Migrate
- db: migration v2 adds barrier_keys table

Also includes: security audit report, CSRF protection, engine design specs
(sshca, transit, user), path-bound AAD migration tool, policy engine
enhancements, and ARCHITECTURE.md updates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/server/server_test.go

@@ -241,18 +241,84 @@ func TestEngineRequestPolicyAllowsWithRule(t *testing.T) {
 	}
 }
 
-// TestOperationAction verifies the read/write classification of operations.
-func TestOperationAction(t *testing.T) {
-	readOps := []string{"list-issuers", "list-certs", "get-cert", "get-root", "get-chain", "get-issuer"}
-	for _, op := range readOps {
-		if got := operationAction(op); got != "read" {
-			t.Errorf("operationAction(%q) = %q, want %q", op, got, "read")
+// TestEngineRequestAdminOnlyBlocksNonAdmin verifies that admin-only operations
+// via the generic endpoint are rejected for non-admin users.
+func TestEngineRequestAdminOnlyBlocksNonAdmin(t *testing.T) {
+	srv, sealMgr, _ := setupTestServer(t)
+	unsealServer(t, sealMgr, nil)
+
+	for _, op := range []string{"create-issuer", "delete-cert", "create-key", "rotate-key", "create-profile", "provision"} {
+		body := makeEngineRequest("test-mount", op)
+		req := httptest.NewRequest(http.MethodPost, "/v1/engine/request", strings.NewReader(body))
+		req = withTokenInfo(req, &auth.TokenInfo{Username: "alice", Roles: []string{"user"}, IsAdmin: false})
+		w := httptest.NewRecorder()
+		srv.handleEngineRequest(w, req)
+
+		if w.Code != http.StatusForbidden {
+			t.Errorf("operation %q: expected 403 for non-admin, got %d", op, w.Code)
 		}
 	}
-	writeOps := []string{"issue", "renew", "create-issuer", "delete-issuer", "sign-csr", "revoke"}
-	for _, op := range writeOps {
-		if got := operationAction(op); got != "write" {
-			t.Errorf("operationAction(%q) = %q, want %q", op, got, "write")
+}
+
+// TestEngineRequestAdminOnlyAllowsAdmin verifies that admin-only operations
+// via the generic endpoint are allowed for admin users.
+func TestEngineRequestAdminOnlyAllowsAdmin(t *testing.T) {
+	srv, sealMgr, _ := setupTestServer(t)
+	unsealServer(t, sealMgr, nil)
+
+	for _, op := range []string{"create-issuer", "delete-cert", "create-key", "rotate-key", "create-profile", "provision"} {
+		body := makeEngineRequest("test-mount", op)
+		req := httptest.NewRequest(http.MethodPost, "/v1/engine/request", strings.NewReader(body))
+		req = withTokenInfo(req, &auth.TokenInfo{Username: "admin", Roles: []string{"admin"}, IsAdmin: true})
+		w := httptest.NewRecorder()
+		srv.handleEngineRequest(w, req)
+
+		// Admin passes the admin check; will get 404 (mount not found) not 403.
+		if w.Code == http.StatusForbidden {
+			t.Errorf("operation %q: admin should not be forbidden, got 403", op)
+		}
+	}
+}
+
+// TestOperationAction verifies the action classification of operations.
+func TestOperationAction(t *testing.T) {
+	tests := map[string]string{
+		// Read operations.
+		"list-issuers":  policy.ActionRead,
+		"list-certs":    policy.ActionRead,
+		"get-cert":      policy.ActionRead,
+		"get-root":      policy.ActionRead,
+		"get-chain":     policy.ActionRead,
+		"get-issuer":    policy.ActionRead,
+		"list-keys":     policy.ActionRead,
+		"get-key":       policy.ActionRead,
+		"get-public-key": policy.ActionRead,
+		"list-users":    policy.ActionRead,
+		"get-profile":   policy.ActionRead,
+		"list-profiles": policy.ActionRead,
+
+		// Granular crypto operations (including batch variants).
+		"encrypt":       policy.ActionEncrypt,
+		"batch-encrypt": policy.ActionEncrypt,
+		"decrypt":       policy.ActionDecrypt,
+		"batch-decrypt": policy.ActionDecrypt,
+		"sign":      policy.ActionSign,
+		"sign-host": policy.ActionSign,
+		"sign-user": policy.ActionSign,
+		"verify":    policy.ActionVerify,
+		"hmac":      policy.ActionHMAC,
+
+		// Write operations.
+		"issue":          policy.ActionWrite,
+		"renew":          policy.ActionWrite,
+		"create-issuer":  policy.ActionWrite,
+		"delete-issuer":  policy.ActionWrite,
+		"sign-csr":       policy.ActionWrite,
+		"revoke":         policy.ActionWrite,
+	}
+	for op, want := range tests {
+		if got := operationAction(op); got != want {
+			t.Errorf("operationAction(%q) = %q, want %q", op, got, want)
 		}
 	}
 }