addition Stripe payment integration work

Feat discrete accounts

backend-go/README.md

@@ -2,7 +2,6 @@ Start DB:
 
 brew services start postgresql@15
 
-
 From the backend-go directory, you have a few options:
 
 Option 1: Single command (both API + poller)
@@ -13,3 +12,9 @@ Terminal 1 (API server):
 cd /Users/kjannette/workspace/koin_ping_0.2.0/backend-go go run ./cmd/api
 Terminal 2 (Poller):
 cd /Users/kjannette/workspace/koin_ping_0.2.0/backend-go go run ./cmd/poller
+
+make run — Builds and runs the API server.
+make dev — Runs the API server with auto-reload via air (falls back to go run if air isn't installed).
+make poller — Builds and runs the poller.
+make poller-dev — Runs the poller with auto-reload.
+make dev-all — Runs both the API and poller concurrently.

backend-go/cmd/api/main.go

@@ -44,6 +44,7 @@ func main() {
 
 	defer database.Close()
 
+	userModel := models.NewUserModel(pool)
 	addressModel := models.NewAddressModel(pool)
 	alertRuleModel := models.NewAlertRuleModel(pool)
 	alertEventModel := models.NewAlertEventModel(pool)
@@ -60,6 +61,15 @@ func main() {
 	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel, cfg)
 	emailDigestHandler := handlers.NewEmailDigestHandler(emailDigestSvc, notifConfigModel)
 	statusHandler := handlers.NewStatusHandler(checkpointModel)
+	stripeHandler := handlers.NewStripeHandler(userModel, cfg)
+
+	authenticate := middleware.Authenticate(userModel)
+	requireSub := middleware.RequireSubscription(userModel)
+
+	// authAndSub chains authentication + subscription check for protected routes.
+	authAndSub := func(h http.Handler) http.Handler {
+		return authenticate(requireSub(h))
+	}
 
 	mux := http.NewServeMux()
 	b := cfg.APIBasePath // e.g. "/v1"
@@ -68,45 +78,54 @@ func main() {
 	mux.HandleFunc("GET "+b+"/health", handlers.HealthCheck)
 	mux.HandleFunc("GET "+b+"/status", statusHandler.GetStatus)
 
-	// Authenticated routes — addresses
+	// Stripe webhook (public — called by Stripe, not authenticated)
+	mux.HandleFunc("POST "+b+"/stripe/webhook", stripeHandler.HandleWebhook)
+
+	// Stripe routes (auth required, NO subscription required)
+	mux.Handle("POST "+b+"/stripe/create-checkout-session",
+		authenticate(http.HandlerFunc(stripeHandler.CreateCheckoutSession)))
+	mux.Handle("GET "+b+"/stripe/subscription-status",
+		authenticate(http.HandlerFunc(stripeHandler.GetSubscriptionStatus)))
+
+	// Authenticated + subscribed routes — addresses
 	mux.Handle("POST "+b+"/addresses",
-		middleware.Authenticate(http.HandlerFunc(addressHandler.Create)))
+		authAndSub(http.HandlerFunc(addressHandler.Create)))
 	mux.Handle("GET "+b+"/addresses",
-		middleware.Authenticate(http.HandlerFunc(addressHandler.List)))
+		authAndSub(http.HandlerFunc(addressHandler.List)))
 	mux.Handle("DELETE "+b+"/addresses/{addressId}",
-		middleware.Authenticate(http.HandlerFunc(addressHandler.Remove)))
+		authAndSub(http.HandlerFunc(addressHandler.Remove)))
 	mux.Handle("PATCH "+b+"/addresses/{addressId}",
-		middleware.Authenticate(http.HandlerFunc(addressHandler.UpdateLabel)))
+		authAndSub(http.HandlerFunc(addressHandler.UpdateLabel)))
 
-	// Authenticated routes for alert rules
+	// Authenticated + subscribed routes — alert rules
 	mux.Handle("POST "+b+"/addresses/{addressId}/alerts",
-		middleware.Authenticate(http.HandlerFunc(alertRuleHandler.Create)))
+		authAndSub(http.HandlerFunc(alertRuleHandler.Create)))
 	mux.Handle("GET "+b+"/addresses/{addressId}/alerts",
-		middleware.Authenticate(http.HandlerFunc(alertRuleHandler.ListByAddress)))
+		authAndSub(http.HandlerFunc(alertRuleHandler.ListByAddress)))
 	mux.Handle("PATCH "+b+"/alerts/{alertId}",
-		middleware.Authenticate(http.HandlerFunc(alertRuleHandler.UpdateStatus)))
+		authAndSub(http.HandlerFunc(alertRuleHandler.UpdateStatus)))
 	mux.Handle("DELETE "+b+"/alerts/{alertId}",
-		middleware.Authenticate(http.HandlerFunc(alertRuleHandler.Remove)))
+		authAndSub(http.HandlerFunc(alertRuleHandler.Remove)))
 
-	// Authenticated routes — alert events
+	// Authenticated + subscribed routes — alert events
 	mux.Handle("GET "+b+"/alert-events",
-		middleware.Authenticate(http.HandlerFunc(alertEventHandler.List)))
+		authAndSub(http.HandlerFunc(alertEventHandler.List)))
 
-	// Authenticated routes — notification config
+	// Authenticated + subscribed routes — notification config
 	mux.Handle("GET "+b+"/notification-config",
-		middleware.Authenticate(http.HandlerFunc(notifConfigHandler.GetConfig)))
+		authAndSub(http.HandlerFunc(notifConfigHandler.GetConfig)))
 	mux.Handle("PUT "+b+"/notification-config",
-		middleware.Authenticate(http.HandlerFunc(notifConfigHandler.UpdateConfig)))
+		authAndSub(http.HandlerFunc(notifConfigHandler.UpdateConfig)))
 	mux.Handle("DELETE "+b+"/notification-config",
-		middleware.Authenticate(http.HandlerFunc(notifConfigHandler.DeleteConfig)))
+		authAndSub(http.HandlerFunc(notifConfigHandler.DeleteConfig)))
 	mux.Handle("POST "+b+"/notification-config/test",
-		middleware.Authenticate(http.HandlerFunc(notifConfigHandler.TestChannels)))
+		authAndSub(http.HandlerFunc(notifConfigHandler.TestChannels)))
 
-	// Authenticated routes — email digest
+	// Authenticated + subscribed routes — email digest
 	mux.Handle("POST "+b+"/email/setup",
-		middleware.Authenticate(http.HandlerFunc(emailDigestHandler.SetupEmail)))
+		authAndSub(http.HandlerFunc(emailDigestHandler.SetupEmail)))
 	mux.Handle("POST "+b+"/email/digest",
-		middleware.Authenticate(http.HandlerFunc(emailDigestHandler.SendDigest)))
+		authAndSub(http.HandlerFunc(emailDigestHandler.SendDigest)))
 
 	handler := corsMiddleware(mux)
 

backend-go/go.mod

@@ -44,6 +44,7 @@ require (
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
 	github.com/resend/resend-go/v3 v3.1.1 // indirect
 	github.com/spiffe/go-spiffe/v2 v2.6.0 // indirect
+	github.com/stripe/stripe-go/v82 v82.5.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/contrib/detectors/gcp v1.39.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.61.0 // indirect

backend-go/go.sum

@@ -101,6 +101,8 @@ github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UV
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/stripe/stripe-go/v82 v82.5.1 h1:05q6ZDKoe8PLMpQV072obF74HCgP4XJeJYoNuRSX2+8=
+github.com/stripe/stripe-go/v82 v82.5.1/go.mod h1:majCQX6AfObAvJiHraPi/5udwHi4ojRvJnnxckvHrX8=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
 go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=

backend-go/infra/migrations/005_create_users_table.sql

@@ -0,0 +1,13 @@
+-- Migration 005: Create users table with UUID primary key
+-- This establishes a local user record for each Firebase-authenticated user.
+
+CREATE TABLE IF NOT EXISTS users (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  firebase_uid VARCHAR(128) NOT NULL UNIQUE,
+  email VARCHAR(255) NOT NULL,
+  display_name VARCHAR(255),
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_users_firebase_uid ON users(firebase_uid);

backend-go/infra/migrations/006_migrate_user_ids_to_uuid.sql

@@ -0,0 +1,73 @@
+-- Migration 006: Migrate user_id columns from Firebase UID strings to user UUIDs
+--
+-- Prerequisites: migration 005 (users table) must be applied first.
+-- This migration backfills the users table from existing data, then swaps the
+-- VARCHAR user_id columns for UUID foreign keys referencing users(id).
+
+BEGIN;
+
+-- 1. Backfill users table from existing Firebase UIDs in addresses
+INSERT INTO users (firebase_uid, email)
+  SELECT DISTINCT user_id, ''
+  FROM addresses
+  WHERE user_id IS NOT NULL
+ON CONFLICT (firebase_uid) DO NOTHING;
+
+-- 2. Backfill from notification configs (catches users with configs but no addresses)
+INSERT INTO users (firebase_uid, email)
+  SELECT DISTINCT user_id, ''
+  FROM user_notification_configs
+  WHERE user_id IS NOT NULL
+ON CONFLICT (firebase_uid) DO NOTHING;
+
+-- ============================================================
+-- 3. Migrate addresses.user_id from VARCHAR to UUID
+-- ============================================================
+
+ALTER TABLE addresses ADD COLUMN user_uuid UUID;
+
+UPDATE addresses a
+SET user_uuid = u.id
+FROM users u
+WHERE u.firebase_uid = a.user_id;
+
+-- Drop old constraints and column
+ALTER TABLE addresses DROP CONSTRAINT IF EXISTS addresses_user_id_address_key;
+DROP INDEX IF EXISTS idx_addresses_user_id;
+ALTER TABLE addresses DROP COLUMN user_id;
+
+-- Rename and constrain
+ALTER TABLE addresses RENAME COLUMN user_uuid TO user_id;
+ALTER TABLE addresses ALTER COLUMN user_id SET NOT NULL;
+ALTER TABLE addresses ADD CONSTRAINT fk_addresses_user
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+ALTER TABLE addresses ADD CONSTRAINT addresses_user_id_address_key
+  UNIQUE (user_id, address);
+CREATE INDEX idx_addresses_user_id ON addresses(user_id);
+
+-- ============================================================
+-- 4. Migrate user_notification_configs.user_id from VARCHAR to UUID
+-- ============================================================
+
+-- Drop the PK first (it's on user_id)
+ALTER TABLE user_notification_configs DROP CONSTRAINT IF EXISTS user_notification_configs_pkey;
+DROP INDEX IF EXISTS idx_notification_configs_enabled;
+
+ALTER TABLE user_notification_configs ADD COLUMN user_uuid UUID;
+
+UPDATE user_notification_configs nc
+SET user_uuid = u.id
+FROM users u
+WHERE u.firebase_uid = nc.user_id;
+
+ALTER TABLE user_notification_configs DROP COLUMN user_id;
+ALTER TABLE user_notification_configs RENAME COLUMN user_uuid TO user_id;
+ALTER TABLE user_notification_configs ALTER COLUMN user_id SET NOT NULL;
+ALTER TABLE user_notification_configs ADD CONSTRAINT user_notification_configs_pkey
+  PRIMARY KEY (user_id);
+ALTER TABLE user_notification_configs ADD CONSTRAINT fk_notification_configs_user
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
+CREATE INDEX idx_notification_configs_enabled
+  ON user_notification_configs(notification_enabled);
+
+COMMIT;

backend-go/infra/migrations/007_add_stripe_to_users.sql

@@ -0,0 +1,8 @@
+-- Migration 007: Add Stripe subscription fields to users table
+
+ALTER TABLE users ADD COLUMN IF NOT EXISTS stripe_customer_id VARCHAR(255);
+ALTER TABLE users ADD COLUMN IF NOT EXISTS stripe_subscription_id VARCHAR(255);
+ALTER TABLE users ADD COLUMN IF NOT EXISTS subscription_status VARCHAR(50) DEFAULT 'none';
+ALTER TABLE users ADD COLUMN IF NOT EXISTS subscription_created_at TIMESTAMP;
+
+CREATE INDEX IF NOT EXISTS idx_users_stripe_customer_id ON users(stripe_customer_id);

backend-go/infra/schema.sql

@@ -4,15 +4,28 @@ DROP TABLE IF EXISTS alert_rules CASCADE;
 DROP TABLE IF EXISTS address_checkpoints CASCADE;
 DROP TABLE IF EXISTS user_notification_configs CASCADE;
 DROP TABLE IF EXISTS addresses CASCADE;
+DROP TABLE IF EXISTS users CASCADE;
+
+CREATE TABLE users (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  firebase_uid VARCHAR(128) NOT NULL UNIQUE,
+  email VARCHAR(255) NOT NULL,
+  display_name VARCHAR(255),
+  stripe_customer_id VARCHAR(255),
+  stripe_subscription_id VARCHAR(255),
+  subscription_status VARCHAR(50) DEFAULT 'none',
+  subscription_created_at TIMESTAMP,
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
 
 CREATE TABLE addresses (
   id SERIAL PRIMARY KEY,
-  user_id VARCHAR(128) NOT NULL,       -- Firebase user ID (multi-user support)
+  user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
   address VARCHAR(42) NOT NULL,        -- Ethereum address format (0x + 40 hex chars)
   label VARCHAR(255),                  -- Optional human-readable label
   created_at TIMESTAMP DEFAULT NOW(),
 
-  -- Unique users can track the same address independently
   UNIQUE(user_id, address)
 );
 
@@ -51,7 +64,7 @@ CREATE TABLE address_checkpoints (
 );
 
 CREATE TABLE user_notification_configs (
-  user_id VARCHAR(128) PRIMARY KEY,
+  user_id UUID PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
   discord_webhook_url TEXT,            -- Discord webhook URL (nullable)
   telegram_chat_id VARCHAR(128),       -- Telegram chat ID (nullable)
   telegram_bot_token VARCHAR(255),     -- Telegram bot token (nullable)
@@ -63,6 +76,8 @@ CREATE TABLE user_notification_configs (
 );
 
 -- Create indexes for common queries
+CREATE INDEX idx_users_firebase_uid ON users(firebase_uid);
+CREATE INDEX idx_users_stripe_customer_id ON users(stripe_customer_id);
 CREATE INDEX idx_addresses_user_id ON addresses(user_id);
 CREATE INDEX idx_alert_rules_address_id ON alert_rules(address_id);
 CREATE INDEX idx_alert_rules_enabled ON alert_rules(enabled);

backend-go/internal/config/config.go

@@ -32,6 +32,11 @@ type Config struct {
 	ResendAPIKey         string
 	EmailFrom            string
 	DigestIntervalHours  int
+	StripeSecretKey      string
+	StripeWebhookSecret  string
+	StripePriceID        string
+	StripePublishableKey string
+	FrontendURL          string
 }
 
 // Load reads configuration from environment variables and returns a Config.
@@ -52,6 +57,11 @@ func Load() (*Config, error) {
 		ResendAPIKey:        os.Getenv("RESEND_API_KEY"),
 		EmailFrom:           getEnv("EMAIL_FROM", "Koin Ping <alerts@koinping.com>"),
 		DigestIntervalHours:  getEnvInt("DIGEST_INTERVAL_HOURS", defaultDigestIntervalHours),
+		StripeSecretKey:      os.Getenv("STRIPE_SECRET_KEY"),
+		StripeWebhookSecret:  os.Getenv("STRIPE_WEBHOOK_SECRET"),
+		StripePriceID:        os.Getenv("STRIPE_PRICE_ID"),
+		StripePublishableKey: os.Getenv("STRIPE_PUBLISHABLE_KEY"),
+		FrontendURL:          getEnv("FRONTEND_URL", "http://localhost:3000"),
 	}
 
 	if cfg.PollIntervalMS < minPollIntervalMS {

backend-go/internal/domain/types.go

@@ -2,6 +2,19 @@ package domain
 
 import "time"
 
+type User struct {
+	ID                    string     `json:"id"`
+	FirebaseUID           string     `json:"-"`
+	Email                 string     `json:"email"`
+	DisplayName           *string    `json:"display_name"`           //nolint:tagliatelle
+	StripeCustomerID      *string    `json:"-"`
+	StripeSubscriptionID  *string    `json:"-"`
+	SubscriptionStatus    string     `json:"subscription_status"`    //nolint:tagliatelle
+	SubscriptionCreatedAt *time.Time `json:"subscription_created_at,omitempty"` //nolint:tagliatelle
+	CreatedAt             time.Time  `json:"created_at"`             //nolint:tagliatelle
+	UpdatedAt             time.Time  `json:"updated_at"`             //nolint:tagliatelle
+}
+
 type Address struct {
 	ID        int       `json:"id"`
 	UserID    string    `json:"user_id"`    //nolint:tagliatelle

backend-go/internal/handlers/stripe.go

@@ -0,0 +1,199 @@
+package handlers
+
+import (
+	"encoding/json"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/stripe/stripe-go/v82"
+	checkoutsession "github.com/stripe/stripe-go/v82/checkout/session"
+	"github.com/stripe/stripe-go/v82/webhook"
+
+	"github.com/kjannette/koin-ping/backend-go/internal/config"
+	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
+	"github.com/kjannette/koin-ping/backend-go/internal/models"
+)
+
+const webhookMaxBodyBytes = 65536
+
+type StripeHandler struct {
+	users *models.UserModel
+	cfg   *config.Config
+}
+
+func NewStripeHandler(users *models.UserModel, cfg *config.Config) *StripeHandler {
+	stripe.Key = cfg.StripeSecretKey
+	return &StripeHandler{users: users, cfg: cfg}
+}
+
+// CreateCheckoutSession creates a Stripe Checkout session for the monthly subscription.
+func (h *StripeHandler) CreateCheckoutSession(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	params := &stripe.CheckoutSessionParams{
+		Mode: stripe.String(string(stripe.CheckoutSessionModeSubscription)),
+		LineItems: []*stripe.CheckoutSessionLineItemParams{
+			{
+				Price:    stripe.String(h.cfg.StripePriceID),
+				Quantity: stripe.Int64(1),
+			},
+		},
+		SuccessURL:        stripe.String(h.cfg.FrontendURL + "/subscribe?payment=success&session_id={CHECKOUT_SESSION_ID}"),
+		CancelURL:         stripe.String(h.cfg.FrontendURL + "/subscribe?payment=cancelled"),
+		ClientReferenceID: stripe.String(userID),
+		CustomerEmail:     stripe.String(user.Email),
+	}
+
+	if user.StripeCustomerID != nil && *user.StripeCustomerID != "" {
+		params.Customer = user.StripeCustomerID
+		params.CustomerEmail = nil
+	}
+
+	s, err := checkoutsession.New(params)
+	if err != nil {
+		log.Printf("Failed to create Stripe checkout session: %v", err)
+		writeError(w, http.StatusInternalServerError, "STRIPE_ERROR", "Failed to create checkout session")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"url": s.URL})
+}
+
+// GetSubscriptionStatus returns the current user's subscription state.
+func (h *StripeHandler) GetSubscriptionStatus(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+
+	user, err := h.users.GetByID(r.Context(), userID)
+	if err != nil || user == nil {
+		log.Printf("Failed to get user %s: %v", userID, err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to load user")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"subscription_status":     user.SubscriptionStatus,
+		"subscription_created_at": user.SubscriptionCreatedAt,
+	})
+}
+
+// HandleWebhook processes incoming Stripe webhook events.
+// This endpoint must NOT require authentication (Stripe calls it directly).
+func (h *StripeHandler) HandleWebhook(w http.ResponseWriter, r *http.Request) {
+	payload, err := io.ReadAll(io.LimitReader(r.Body, webhookMaxBodyBytes))
+	if err != nil {
+		log.Printf("Error reading webhook body: %v", err)
+		w.WriteHeader(http.StatusServiceUnavailable)
+		return
+	}
+
+	sig := r.Header.Get("Stripe-Signature")
+	event, err := webhook.ConstructEvent(payload, sig, h.cfg.StripeWebhookSecret)
+	if err != nil {
+		log.Printf("Webhook signature verification failed: %v", err)
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	switch event.Type {
+	case "checkout.session.completed":
+		h.handleCheckoutCompleted(r, event)
+	case "customer.subscription.updated":
+		h.handleSubscriptionUpdated(r, event)
+	case "customer.subscription.deleted":
+		h.handleSubscriptionDeleted(r, event)
+	default:
+		log.Printf("Unhandled Stripe event type: %s", event.Type)
+	}
+
+	w.WriteHeader(http.StatusOK)
+}
+
+func (h *StripeHandler) handleCheckoutCompleted(r *http.Request, event stripe.Event) {
+	var session stripe.CheckoutSession
+	if err := json.Unmarshal(event.Data.Raw, &session); err != nil {
+		log.Printf("Error parsing checkout session: %v", err)
+		return
+	}
+
+	userID := session.ClientReferenceID
+	if userID == "" {
+		log.Println("Checkout session missing client_reference_id")
+		return
+	}
+
+	customerID := ""
+	if session.Customer != nil {
+		customerID = session.Customer.ID
+	}
+	subscriptionID := ""
+	if session.Subscription != nil {
+		subscriptionID = session.Subscription.ID
+	}
+
+	if customerID != "" {
+		if err := h.users.UpdateStripeCustomer(r.Context(), userID, customerID); err != nil {
+			log.Printf("Failed to save Stripe customer ID: %v", err)
+		}
+	}
+
+	if subscriptionID != "" && customerID != "" {
+		if err := h.users.ActivateSubscription(r.Context(), customerID, subscriptionID, "active"); err != nil {
+			log.Printf("Failed to activate subscription: %v", err)
+		}
+	}
+
+	log.Printf("Checkout completed for user %s, customer %s, subscription %s", userID, customerID, subscriptionID)
+}
+
+func (h *StripeHandler) handleSubscriptionUpdated(r *http.Request, event stripe.Event) {
+	var sub stripe.Subscription
+	if err := json.Unmarshal(event.Data.Raw, &sub); err != nil {
+		log.Printf("Error parsing subscription update: %v", err)
+		return
+	}
+
+	customerID := ""
+	if sub.Customer != nil {
+		customerID = sub.Customer.ID
+	}
+	if customerID == "" {
+		return
+	}
+
+	status := string(sub.Status)
+	if err := h.users.ActivateSubscription(r.Context(), customerID, sub.ID, status); err != nil {
+		log.Printf("Failed to update subscription status: %v", err)
+	}
+
+	log.Printf("Subscription %s updated to %s for customer %s", sub.ID, status, customerID)
+}
+
+func (h *StripeHandler) handleSubscriptionDeleted(r *http.Request, event stripe.Event) {
+	var sub stripe.Subscription
+	if err := json.Unmarshal(event.Data.Raw, &sub); err != nil {
+		log.Printf("Error parsing subscription deletion: %v", err)
+		return
+	}
+
+	customerID := ""
+	if sub.Customer != nil {
+		customerID = sub.Customer.ID
+	}
+	if customerID == "" {
+		return
+	}
+
+	if err := h.users.UpdateSubscriptionStatus(r.Context(), customerID, "canceled"); err != nil {
+		log.Printf("Failed to mark subscription canceled: %v", err)
+	}
+
+	log.Printf("Subscription canceled for customer %s", customerID)
+}

backend-go/internal/middleware/auth.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	fbauth "github.com/kjannette/koin-ping/backend-go/internal/firebase"
+	"github.com/kjannette/koin-ping/backend-go/internal/models"
 )
 
 type contextKey string
@@ -26,10 +27,14 @@ type errorResponse struct {
 func writeJSON(w http.ResponseWriter, status int, v interface{}) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(v)
+	json.NewEncoder(w).Encode(v) //nolint:errcheck
 }
 
-func Authenticate(next http.Handler) http.Handler {
+// Authenticate verifies the Firebase ID token and auto-provisions a local user
+// record. The local user UUID (not the Firebase UID) is placed into context so
+// all downstream handlers use it as the canonical user identifier.
+func Authenticate(userModel *models.UserModel) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			authHeader := r.Header.Get("Authorization")
 			if authHeader == "" || !strings.HasPrefix(authHeader, "Bearer ") {
@@ -72,17 +77,65 @@ func Authenticate(next http.Handler) http.Handler {
 				return
 			}
 
-		userID := decoded.UID
+			firebaseUID := decoded.UID
 			email, _ := decoded.Claims["email"].(string)
 
-		log.Printf("Token verified! User ID: %s, Email: %s", userID, email)
+			user, err := userModel.FindOrCreateByFirebaseUID(r.Context(), firebaseUID, email)
+			if err != nil {
+				log.Printf("Failed to provision local user for Firebase UID %s: %v", firebaseUID, err)
+				writeJSON(w, http.StatusInternalServerError, errorResponse{
+					Error:   "INTERNAL_ERROR",
+					Message: "Failed to initialize user account",
+				})
+				return
+			}
 
-		ctx := context.WithValue(r.Context(), UserIDKey, userID)
+			log.Printf("Token verified! User UUID: %s, Email: %s", user.ID, email)
+
+			ctx := context.WithValue(r.Context(), UserIDKey, user.ID)
 			ctx = context.WithValue(ctx, UserEmailKey, email)
 
 			next.ServeHTTP(w, r.WithContext(ctx))
 		})
 	}
+}
+
+// RequireSubscription blocks requests from users without an active subscription.
+// Must be applied after Authenticate.
+func RequireSubscription(userModel *models.UserModel) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			userID := GetUserID(r.Context())
+			if userID == "" {
+				writeJSON(w, http.StatusUnauthorized, errorResponse{
+					Error:   "UNAUTHORIZED",
+					Message: "Authentication required",
+				})
+				return
+			}
+
+			user, err := userModel.GetByID(r.Context(), userID)
+			if err != nil || user == nil {
+				log.Printf("RequireSubscription: failed to load user %s: %v", userID, err)
+				writeJSON(w, http.StatusInternalServerError, errorResponse{
+					Error:   "INTERNAL_ERROR",
+					Message: "Failed to verify subscription",
+				})
+				return
+			}
+
+			if user.SubscriptionStatus != "active" && user.SubscriptionStatus != "trialing" {
+				writeJSON(w, http.StatusForbidden, errorResponse{
+					Error:   "SUBSCRIPTION_REQUIRED",
+					Message: "An active subscription is required to use this feature",
+				})
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}
 
 func GetUserID(ctx context.Context) string {
 	if v, ok := ctx.Value(UserIDKey).(string); ok {

backend-go/internal/models/user.go

@@ -0,0 +1,89 @@
+package models
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+)
+
+type UserModel struct {
+	pool *pgxpool.Pool
+}
+
+func NewUserModel(pool *pgxpool.Pool) *UserModel {
+	return &UserModel{pool: pool}
+}
+
+const userColumns = `id, firebase_uid, email, display_name,
+	stripe_customer_id, stripe_subscription_id, subscription_status,
+	subscription_created_at, created_at, updated_at`
+
+func scanUser(row pgx.Row) (*domain.User, error) {
+	var u domain.User
+	err := row.Scan(
+		&u.ID, &u.FirebaseUID, &u.Email, &u.DisplayName,
+		&u.StripeCustomerID, &u.StripeSubscriptionID, &u.SubscriptionStatus,
+		&u.SubscriptionCreatedAt, &u.CreatedAt, &u.UpdatedAt,
+	)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil //nolint:nilnil
+		}
+		return nil, err
+	}
+	return &u, nil
+}
+
+// FindOrCreateByFirebaseUID returns the local user for a Firebase UID,
+// creating one if it doesn't exist yet. On conflict (returning user) the
+// updated_at timestamp is refreshed.
+func (m *UserModel) FindOrCreateByFirebaseUID(ctx context.Context, firebaseUID, email string) (*domain.User, error) {
+	row := m.pool.QueryRow(ctx,
+		`INSERT INTO users (firebase_uid, email)
+		 VALUES ($1, $2)
+		 ON CONFLICT (firebase_uid) DO UPDATE SET updated_at = NOW()
+		 RETURNING `+userColumns,
+		firebaseUID, email,
+	)
+	return scanUser(row)
+}
+
+func (m *UserModel) GetByID(ctx context.Context, id string) (*domain.User, error) {
+	row := m.pool.QueryRow(ctx,
+		`SELECT `+userColumns+` FROM users WHERE id = $1`, id,
+	)
+	return scanUser(row)
+}
+
+func (m *UserModel) UpdateStripeCustomer(ctx context.Context, userID, stripeCustomerID string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET stripe_customer_id = $2, updated_at = NOW() WHERE id = $1`,
+		userID, stripeCustomerID,
+	)
+	return err
+}
+
+func (m *UserModel) ActivateSubscription(ctx context.Context, stripeCustomerID, subscriptionID, status string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users
+		 SET stripe_subscription_id = $2,
+		     subscription_status = $3,
+		     subscription_created_at = COALESCE(subscription_created_at, NOW()),
+		     updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, subscriptionID, status,
+	)
+	return err
+}
+
+func (m *UserModel) UpdateSubscriptionStatus(ctx context.Context, stripeCustomerID, status string) error {
+	_, err := m.pool.Exec(ctx,
+		`UPDATE users SET subscription_status = $2, updated_at = NOW()
+		 WHERE stripe_customer_id = $1`,
+		stripeCustomerID, status,
+	)
+	return err
+}

frontend/src/App.jsx

@@ -16,7 +16,7 @@ export default function App() {
             <Routes>
                 <Route path="/login" element={<Login />} />
                 <Route path="/signup" element={<Signup />} />
-                <Route path="/onboarding" element={<Onboarding />} />
+                <Route path="/subscribe" element={<Onboarding />} />
                 <Route path="*" element={<Navigate to="/login" />} />
             </Routes>
         );
@@ -30,7 +30,7 @@ export default function App() {
                 <Route path="/addresses" element={<Addresses />} />
                 <Route path="/alerts" element={<Alerts />} />
                 <Route path="/alertevents" element={<AlertHistory />} />
-                <Route path="/onboarding" element={<Onboarding />} />
+                <Route path="/subscribe" element={<Onboarding />} />
                 <Route path="*" element={<Navigate to="/addresses" />} />
             </Routes>
         </div>

frontend/src/api/stripe.jsx

@@ -0,0 +1,27 @@
+import { getAuthHeaders } from "./authHeaders";
+import { API_BASE } from "./config";
+
+export async function createCheckoutSession() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/create-checkout-session`, {
+        method: "POST",
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to create checkout session");
+    }
+    return res.json();
+}
+
+export async function getSubscriptionStatus() {
+    const headers = await getAuthHeaders();
+    const res = await fetch(`${API_BASE}/stripe/subscription-status`, {
+        headers,
+    });
+    if (!res.ok) {
+        const data = await res.json();
+        throw new Error(data.message || "Failed to get subscription status");
+    }
+    return res.json();
+}

frontend/src/components/Input.css

@@ -1,6 +1,6 @@
 .input__label {
   display: block;
-  margin-bottom: 0.4rem;
+  margin: 0.8rem 0rem 0.4rem 0rem;
   font-size: 0.9rem;
 }
 

frontend/src/pages/Login.css

@@ -19,6 +19,8 @@
 .login-heading {
   margin-bottom: 2rem;
   text-align: center;
+  position: relative;
+  top: -20px;
 }
 
 .login-brand {

frontend/src/pages/Onboarding.css

@@ -183,3 +183,56 @@
   margin-bottom: 1.5rem;
   font-size: 0.9rem;
 }
+
+/* Subscribe card (Step 2) */
+.subscribe-card {
+  background-color: var(--color-bg-card, #1a1a2e);
+  border: 1px solid var(--color-border-light);
+  border-radius: var(--radius-lg);
+  padding: 1.5rem;
+  text-align: center;
+  margin-bottom: 1rem;
+}
+
+.subscribe-card__price {
+  margin-bottom: 1.25rem;
+}
+
+.subscribe-card__amount {
+  font-size: 2.5rem;
+  font-weight: 700;
+  color: white;
+}
+
+.subscribe-card__period {
+  font-size: 1rem;
+  color: #888;
+  margin-left: 2px;
+}
+
+.subscribe-card__features {
+  list-style: none;
+  padding: 0;
+  margin: 0 0 1.25rem;
+  text-align: left;
+}
+
+.subscribe-card__features li {
+  padding: 0.35rem 0;
+  color: #ccc;
+  font-size: 0.9rem;
+}
+
+.subscribe-card__features li::before {
+  content: "\2713";
+  color: var(--color-primary);
+  margin-right: 0.6rem;
+  font-weight: bold;
+}
+
+.subscribe-card__commitment {
+  color: #999;
+  font-size: 0.8rem;
+  margin: 0;
+  font-style: italic;
+}

frontend/src/pages/Onboarding.jsx

@@ -1,11 +1,13 @@
 /**
- * Onboarding Wizard
+ * Subscribe / Onboarding Wizard
  *
  * 5-step guided flow: Create Account -> Add Wallet -> Alert Rules -> Notifications -> Done
+ * After account creation, user is redirected to Stripe Checkout for payment.
+ * On successful payment, they return here at step 2 (Add Wallet).
  */
 
 import { useState, useEffect } from "react";
-import { useNavigate } from "react-router-dom";
+import { useNavigate, useSearchParams } from "react-router-dom";
 import { useAuth } from "../contexts/AuthContext";
 import { createAddress, getAddresses } from "../api/addresses";
 import { createAlert } from "../api/alerts";
@@ -13,6 +15,7 @@ import {
     updateNotificationConfig,
     testNotificationChannels,
 } from "../api/notificationConfig";
+import { createCheckoutSession, getSubscriptionStatus } from "../api/stripe";
 import Input from "../components/Input";
 import Button from "../components/Button";
 import "./Onboarding.css";
@@ -28,6 +31,7 @@ const STEPS = [
 export default function Onboarding() {
     const { currentUser, signup } = useAuth();
     const navigate = useNavigate();
+    const [searchParams, setSearchParams] = useSearchParams();
 
     const [step, setStep] = useState(1);
     const [loading, setLoading] = useState(false);
@@ -71,6 +75,20 @@ export default function Onboarding() {
             .catch(() => {});
     }, [currentUser, navigate]);
 
+    // Handle Stripe redirect back from checkout
+    useEffect(() => {
+        if (!currentUser) return;
+        const payment = searchParams.get("payment");
+        if (payment === "success") {
+            setSearchParams({}, { replace: true });
+            setStep(2);
+        } else if (payment === "cancelled") {
+            setSearchParams({}, { replace: true });
+            setStep(1);
+            setError("Payment was cancelled. Please try again.");
+        }
+    }, [currentUser, searchParams, setSearchParams]);
+
     // ── Step handlers ─────────────────────────────────────────────────────────
 
     async function handleStep1() {
@@ -87,10 +105,18 @@ export default function Onboarding() {
             setError("Password must be at least 6 characters");
             return;
         }
-        if (!currentUser) {
         try {
             setLoading(true);
+            if (!currentUser) {
                 await signup(data.email, data.password);
+            }
+            const status = await getSubscriptionStatus();
+            if (status.subscription_status === "active" || status.subscription_status === "trialing") {
+                setStep(2);
+                return;
+            }
+            const { url } = await createCheckoutSession();
+            window.location.href = url;
         } catch (err) {
             if (err.code === "auth/email-already-in-use") {
                 setError("Email already in use. Try logging in instead.");
@@ -102,13 +128,8 @@ export default function Onboarding() {
                 setError("Failed to create account: " + err.message);
             }
             setLoading(false);
-                return;
-            } finally {
-                setLoading(false);
         }
     }
-        setStep(2);
-    }
 
     async function handleStep2() {
         setError("");
@@ -544,7 +565,7 @@ export default function Onboarding() {
         if (step === 5) return null;
 
         const canSkip = step === 3 || step === 4;
-        const canBack = step > 1;
+        const canBack = step > 2;
 
         async function handleNext() {
             setSkipWarning("");
@@ -566,6 +587,12 @@ export default function Onboarding() {
             setStep((s) => s - 1);
         }
 
+        const nextLabel = step === 1
+            ? "Create Account & Subscribe"
+            : step === 4
+              ? "Finish"
+              : "Next →";
+
         return (
             <div className="onboarding__footer">
                 <div>
@@ -595,7 +622,7 @@ export default function Onboarding() {
                         disabled={loading}
                         className="text-bold"
                     >
-                        {loading ? "Please wait..." : step === 4 ? "Finish" : "Next →"}
+                        {loading ? "Please wait..." : nextLabel}
                     </Button>
                 </div>
             </div>
@@ -605,11 +632,11 @@ export default function Onboarding() {
     // ── Render ────────────────────────────────────────────────────────────────
 
     const stepContent = {
-        1: <Step1 />,
-        2: <Step2 />,
-        3: <Step3 />,
-        4: <Step4 />,
-        5: <Step5 />,
+        1: Step1(),
+        2: Step2(),
+        3: Step3(),
+        4: Step4(),
+        5: Step5(),
     };
 
     return (
@@ -617,7 +644,7 @@ export default function Onboarding() {
             <div className="onboarding__container">
                 <h1 className="onboarding__title">Koin Ping</h1>
 
-                <ProgressBar />
+                {ProgressBar()}
 
                 {error && (
                     <div className="alert alert--error">{error}</div>
@@ -629,7 +656,7 @@ export default function Onboarding() {
 
                 <div className="onboarding__card">
                     {stepContent[step]}
-                    <Footer />
+                    {Footer()}
                 </div>
 
                 {step === 1 && (

frontend/src/pages/Signup.jsx

@@ -1,5 +1,5 @@
 import { Navigate } from "react-router-dom";
 
 export default function Signup() {
-    return <Navigate to="/onboarding" replace />;
+    return <Navigate to="/subscribe" replace />;
 }