fix: handle pre-flight requests

go/internal/middleware/cors.go

@@ -0,0 +1,39 @@
+package middleware
+
+import "net/http"
+
+// CORS wraps a handler to add CORS headers and handle preflight requests.
+func CORS(allowedOrigins []string) func(http.Handler) http.Handler {
+	originSet := make(map[string]struct{}, len(allowedOrigins))
+	for _, o := range allowedOrigins {
+		originSet[o] = struct{}{}
+	}
+
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			origin := r.Header.Get("Origin")
+
+			// Check if the origin is allowed (empty allowedOrigins means allow all)
+			allowed := len(originSet) == 0
+			if !allowed {
+				_, allowed = originSet[origin]
+			}
+
+			if allowed && origin != "" {
+				w.Header().Set("Access-Control-Allow-Origin", origin)
+				w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, PATCH, OPTIONS")
+				w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
+				w.Header().Set("Access-Control-Allow-Credentials", "true")
+				w.Header().Set("Access-Control-Max-Age", "86400")
+			}
+
+			// Handle preflight
+			if r.Method == http.MethodOptions {
+				w.WriteHeader(http.StatusNoContent)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}