CORS: Default Preflight Behavior

Rely on the built-in 204 preflight response unless a route truly needs a custom OPTIONS handler.

Rely on the built-in 204 preflight response unless a route truly needs a custom OPTIONS handler.

Last reviewed: 2026-03-06

When to use this

Use this approach when you want a config-first Cloudflare Worker gateway behavior that is already implemented in the repository and covered by tests or canonical examples.

What this does not do

• It does not add unsupported product features such as rate limiting, caching, API keys, analytics, or OpenAPI generation.

• It does not replace upstream application logic that still belongs in your services.

• It does not remove the need to validate environment variables, bindings, and route intent before deploy.

Repo-grounded example

{
  "cors": {
    "allow_origins": ["https://app.example.com"],
    "allow_methods": ["GET", "POST", "OPTIONS"],
    "allow_headers": ["Content-Type", "Authorization", "X-Refresh-Token"],
    "expose_headers": ["X-Request-Id"],
    "allow_credentials": true,
    "max_age": 300
  }
}

This example is grounded in the current implementation shape: JSON config, path-based routing, optional auth, request mapping, and Worker-native integrations.

Troubleshooting

• Confirm the route path and HTTP method match what the worker receives.

• Confirm the config source is the one you expect: local file, KV, or SAG_API_CONFIG_JSON.

• Confirm required bindings and environment variables are present before debugging downstream logic.

• Run the existing tests in the main gateway repo when a config change appears correct but runtime behavior disagrees.

Related docs

• cors

• introduction

• gateway troubleshooting matrix