CORS

What This Skill Does

The CORS skill provides an intelligent, automated assistant to help developers configure Cross-Origin Resource Sharing (CORS) policies. It offers deep insights into preflight triggers, credential management, and origin validation to ensure your web applications communicate securely across domains without encountering common browser blocking errors. It helps you navigate the complexities of Vary: Origin headers, preflight caching (Max-Age), and exposed header requirements, effectively turning a common source of debugging frustration into a systematic, secure process.

Installation

You can install this skill directly via the OpenClaw command-line interface using the following command: clawhub install openclaw/skills/skills/ivangdavila/cors

Use Cases

• Production Hardening: Configure strict origin allowlists and implement secure credential handling to protect APIs from unauthorized cross-origin access.
• API Debugging: Quickly diagnose why your frontend application is blocked from accessing resources, specifically when dealing with custom headers or preflight OPTIONS failures.
• Performance Optimization: Correctly implement Access-Control-Max-Age to cache preflight requests, reducing network overhead for complex API calls.
• Proxy Configuration: Learn how to use the Vary header correctly to prevent CDN and proxy caches from misidentifying cross-origin responses.

Example Prompts

1. "Analyze my server's CORS implementation: I am using Access-Control-Allow-Origin: * but my cookies aren't being sent, what am I doing wrong?"
2. "I'm getting a CORS error when I try to read a custom X-Auth-Token header from my API response. How do I expose this to my frontend?"
3. "Help me write a secure origin validation function for my Express server that prevents the evilexample.com bypass risk."

Tips & Limitations

Always remember that CORS is a browser-level security feature, not a server-side protection mechanism against non-browser clients. Avoid using wildcard origins in production, especially when credentials are involved. Note that browser caps on preflight caching (e.g., 2 hours in Chrome) override higher Access-Control-Max-Age settings. Ensure you are validating origins with anchored regex to prevent substring exploitation. When in doubt, explicitly list your headers in Access-Control-Allow-Headers and Access-Control-Expose-Headers rather than using the * wildcard to ensure maximum compatibility across different browser engines.