fix: restrict CORS to configured origins (closes #40)

- Add CORSOrigins config field (UPAAS_CORS_ORIGINS env var)
- Default to same-origin only (no CORS headers when unconfigured)
- When configured, allow specified origins with AllowCredentials: true
- Add tests for CORS middleware behavior

internal/middleware/middleware.go

@@ -177,17 +177,48 @@ func realIP(r *http.Request) string {
 }
 
 // CORS returns CORS middleware.
+// When UPAAS_CORS_ORIGINS is empty (default), no CORS headers are sent
+// (same-origin only). When configured, only the specified origins are
+// allowed and credentials (cookies) are permitted.
 func (m *Middleware) CORS() func(http.Handler) http.Handler {
+	origins := parseCORSOrigins(m.params.Config.CORSOrigins)
+
+	// No origins configured — no CORS headers (same-origin policy).
+	if len(origins) == 0 {
+		return func(next http.Handler) http.Handler {
+			return next
+		}
+	}
+
 	return cors.Handler(cors.Options{
-		AllowedOrigins:   []string{"*"},
+		AllowedOrigins:   origins,
 		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
 		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "X-CSRF-Token"},
 		ExposedHeaders:   []string{"Link"},
-		AllowCredentials: false,
+		AllowCredentials: true,
 		MaxAge:           corsMaxAge,
 	})
 }
 
+// parseCORSOrigins splits a comma-separated origin string into a slice,
+// trimming whitespace. Returns nil if the input is empty.
+func parseCORSOrigins(raw string) []string {
+	if raw == "" {
+		return nil
+	}
+
+	parts := strings.Split(raw, ",")
+	origins := make([]string, 0, len(parts))
+
+	for _, p := range parts {
+		if o := strings.TrimSpace(p); o != "" {
+			origins = append(origins, o)
+		}
+	}
+
+	return origins
+}
+
 // MetricsAuth returns basic auth middleware for metrics endpoint.
 func (m *Middleware) MetricsAuth() func(http.Handler) http.Handler {
 	if m.params.Config.MetricsUsername == "" {
@@ -235,9 +266,9 @@ func (m *Middleware) CSRF() func(http.Handler) http.Handler {
 // loginRateLimit configures the login rate limiter.
 const (
 	loginRateLimit      = rate.Limit(5.0 / 60.0) // 5 requests per 60 seconds
-	loginBurst          = 5                       // allow burst of 5
-	limiterExpiry       = 10 * time.Minute        // evict entries not seen in 10 minutes
-	limiterCleanupEvery = 1 * time.Minute         // sweep interval
+	loginBurst          = 5                      // allow burst of 5
+	limiterExpiry       = 10 * time.Minute       // evict entries not seen in 10 minutes
+	limiterCleanupEvery = 1 * time.Minute        // sweep interval
 )
 
 // ipLimiterEntry stores a rate limiter with its last-seen timestamp.
@@ -249,8 +280,8 @@ type ipLimiterEntry struct {
 // ipLimiter tracks per-IP rate limiters for login attempts with automatic
 // eviction of stale entries to prevent unbounded memory growth.
 type ipLimiter struct {
-	mu       sync.Mutex
-	limiters map[string]*ipLimiterEntry
+	mu        sync.Mutex
+	limiters  map[string]*ipLimiterEntry
 	lastSweep time.Time
 }