fix(webhook): fail closed when stripe webhook secret is not set

api/handlers/webhook.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"log/slog"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -52,8 +53,17 @@ func (h *WebhookHandler) HandleStripe(w http.ResponseWriter, r *http.Request) {
 
 	// Verify the Stripe signature. Reject anything that doesn't match.
 	if h.webhookSecret == "" {
-		// No secret configured — log a loud warning but still process in dev.
-		webhookLog().Warn("stripe webhook secret not set; skipping signature verification")
+		// Fail closed in production. config.validate() requires STRIPE_WEBHOOK_SECRET
+		// in production, so the server should never boot into this state; this is
+		// defense in depth against a misconfigured deploy. Mirrors the Shippo and
+		// Slack handlers, which already refuse to run without their secret.
+		if os.Getenv("ENVIRONMENT") == "production" {
+			webhookLog().Error("stripe webhook secret not set in production; refusing to process event")
+			utils.RespondError(w, http.StatusServiceUnavailable, "WEBHOOK_NOT_CONFIGURED", "webhook verification not configured", nil)
+			return
+		}
+		// Development only; warn loudly but still process so local testing works.
+		webhookLog().Warn("stripe webhook secret not set; skipping signature verification (development only)")
 	} else {
 		sig := r.Header.Get("Stripe-Signature")
 		if _, err := webhook.ConstructEventWithOptions(body, sig, h.webhookSecret, webhook.ConstructEventOptions{
@@ -124,6 +134,20 @@ func (h *WebhookHandler) handlePaymentIntentSucceeded(ctx context.Context, event
 		return
 	}
 
+	// Defense in depth: even behind a valid signature, refuse to mark an order
+	// paid unless the PaymentIntent's amount and currency match what we charged.
+	// Under ConvertCart these always match (Amount == order.Total at creation), so
+	// a mismatch means a malformed or unexpected event we should not trust.
+	if pi.Amount != int64(order.Total) {
+		webhookLog().Error("payment intent amount mismatch; refusing to mark paid", "order_id", orderIDStr, "pi", pi.ID, "pi_amount", pi.Amount, "order_total", order.Total)
+		return
+	}
+	if pi.Currency != "" && pi.Currency != stripe.CurrencyUSD {
+		webhookLog().Error("payment intent currency mismatch; refusing to mark paid",
+			"order_id", orderIDStr, "pi", pi.ID, "currency", string(pi.Currency))
+		return
+	}
+
 	txErr := db.Transaction(func(tx *gorm.DB) error {
 		if err := tx.Model(&order).Updates(map[string]any{
 			"status":            models.OrderStatusPaid,

api/handlers/webhook_test.go

@@ -222,3 +222,38 @@ func TestHandlePaymentIntentSucceeded_RequiresActionFlipsToPaid(t *testing.T) {
 		t.Fatalf("stripe_payment_id: want %q, got %q", order.StripePaymentID, reloaded.StripePaymentID)
 	}
 }
+
+func TestHandlePaymentIntentSucceeded_AmountMismatchDoesNotPay(t *testing.T) {
+	testDB, user := setupCartTestDB(t)
+	defer func() { _ = os.Remove(testDB) }()
+	defer database.ResetForTesting()
+
+	order := seedOrderForWebhook(t, user.ID, models.OrderStatusRequiresAction, "pi_test_amount_mismatch")
+
+	// PI claims 1 cent; seed order.Total is 500.
+	pi := map[string]any{
+		"id":       order.StripePaymentID,
+		"amount":   1,
+		"metadata": map[string]string{"order_id": fmt.Sprintf("%d", order.ID)},
+	}
+	raw, err := json.Marshal(pi)
+	if err != nil {
+		t.Fatalf("marshal pi: %v", err)
+	}
+	evt := stripe.Event{
+		Type: "payment_intent.succeeded",
+		Data: &stripe.EventData{Raw: raw},
+	}
+
+	h := NewWebhookHandler("", "")
+	h.handlePaymentIntentSucceeded(context.Background(), evt)
+
+	db := database.GetDB()
+	var reloaded models.Order
+	if err := db.First(&reloaded, order.ID).Error; err != nil {
+		t.Fatalf("reloaded order: %v", err)
+	}
+	if reloaded.Status == models.OrderStatusPaid {
+		t.Fatalf("order marked paid despite amount mismatch")
+	}
+}

pkg/config/config.go

@@ -92,6 +92,7 @@ func (c *Config) validate() error {
 		{"JWT_SECRET", c.JWTSecret},
 		{"STRIPE_SECRET_KEY", c.StripeSecretKey},
 		{"AUTH_FINGERPRINT_KEY", c.AuthFingerprintKey},
+		{"STRIPE_WEBHOOK_SECRET", c.StripeWebhookSecret},
 	}
 
 	var missing []string