feat(admin): Paddle webhook ingress — verify, idempotent claim, dispatch

admin/internal/api/paddle.go

@@ -0,0 +1,64 @@
+package api
+
+import (
+	"encoding/json"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/mrhid6/vantage/admin/internal/billing"
+	"github.com/mrhid6/vantage/admin/internal/config"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
+)
+
+// paddleWebhook is the ingress for every Paddle event.
+//
+// Order is load-bearing: read the RAW body first (the signature is over the
+// exact bytes), verify, THEN claim the event ID, THEN dispatch. A bad signature
+// is 401 and processes nothing; a duplicate of a handled event is 200 and does
+// nothing; a handler error is 500 so Paddle retries, and is recorded for staff.
+func paddleWebhook(cfg config.Config) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		body, err := io.ReadAll(c.Request.Body)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "unreadable body"})
+			return
+		}
+		if !paddle.VerifySignature(cfg.PaddleWebhookSecret,
+			c.GetHeader("Paddle-Signature"), body) {
+			log.Printf("paddle webhook: bad signature from %s", c.ClientIP())
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "bad signature"})
+			return
+		}
+
+		var ev billing.Event
+		if err := json.Unmarshal(body, &ev); err != nil || ev.EventID == "" {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "malformed event"})
+			return
+		}
+
+		ctx := c.Request.Context()
+		claimed, err := models.ClaimEvent(ctx, ev.EventID, ev.EventType)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "claim failed"})
+			return
+		}
+		if !claimed {
+			// Already handled (or in flight). 200 so Paddle stops retrying.
+			c.JSON(http.StatusOK, gin.H{"duplicate": true})
+			return
+		}
+
+		if err := billing.Dispatch(ctx, ev); err != nil {
+			log.Printf("paddle webhook: handler %s failed for %s: %v",
+				ev.EventType, ev.EventID, err)
+			_ = models.MarkEventProcessed(ctx, ev.EventID, err)
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "handler failed"})
+			return
+		}
+		_ = models.MarkEventProcessed(ctx, ev.EventID, nil)
+		c.JSON(http.StatusOK, gin.H{"ok": true})
+	}
+}

admin/internal/api/routes.go

@@ -39,6 +39,10 @@ func Routes(cfg config.Config) http.Handler {
 	r.POST("/auth/signup", auth.HandleSignup)
 	r.POST("/auth/accept-invite", auth.HandleAcceptInvite)
 
+	// Public: Paddle carries no session cookie; its signature is its auth. Must
+	// NOT sit under the cust group's session middleware.
+	r.POST("/api/paddle/webhook", paddleWebhook(cfg))
+
 	cust := r.Group("/api")
 	cust.Use(auth.RequireCustomer())
 	{

admin/internal/billing/events.go

@@ -0,0 +1,59 @@
+// Package billing turns verified Paddle webhooks into licence actions. It never
+// verifies signatures (that is paddle.VerifySignature at the edge) and never
+// signs (that is licensing.Issue); it decides what a subscription's current
+// state means and calls the issuer.
+package billing
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// Event is the decoded Paddle webhook envelope. Data is left raw so each handler
+// decodes only the shape it needs.
+type Event struct {
+	EventID    string          `json:"event_id"`
+	EventType  string          `json:"event_type"`
+	OccurredAt time.Time       `json:"occurred_at"`
+	Data       json.RawMessage `json:"data"`
+}
+
+// Dispatch routes one event to its handler. Unknown event types are a no-op
+// success: Paddle sends many we do not care about, and 200 stops it retrying.
+func Dispatch(ctx context.Context, ev Event) error {
+	switch ev.EventType {
+	case "subscription.created", "subscription.updated", "subscription.activated":
+		return handleSubscription(ctx, ev)
+	case "subscription.canceled":
+		return handleCanceled(ctx, ev)
+	case "subscription.past_due":
+		return handlePastDue(ctx, ev)
+	case "transaction.completed":
+		return handleTransactionCompleted(ctx, ev)
+	case "transaction.payment_failed":
+		return handlePaymentFailed(ctx, ev)
+	case "customer.updated":
+		return handleCustomerUpdated(ctx, ev)
+	default:
+		return nil
+	}
+}
+
+// decode is a small helper so every handler decodes Data the same way.
+func decode[T any](ev Event) (T, error) {
+	var v T
+	if err := json.Unmarshal(ev.Data, &v); err != nil {
+		return v, fmt.Errorf("decode %s: %w", ev.EventType, err)
+	}
+	return v, nil
+}
+
+// Stubs replaced in tasks 3 and 4.
+func handleSubscription(ctx context.Context, ev Event) error         { return nil }
+func handleCanceled(ctx context.Context, ev Event) error             { return nil }
+func handlePastDue(ctx context.Context, ev Event) error              { return nil }
+func handleTransactionCompleted(ctx context.Context, ev Event) error { return nil }
+func handlePaymentFailed(ctx context.Context, ev Event) error        { return nil }
+func handleCustomerUpdated(ctx context.Context, ev Event) error      { return nil }