Add CORS middleware plugin

[0xReLogic]

Description

Add a CORS (Cross-Origin Resource Sharing) middleware plugin to handle cross-origin requests.

Requirements

• Implement CORS plugin in internal/plugins/cors/
• Support configurable allowed origins, methods, and headers
• Handle preflight OPTIONS requests
• Add to plugin chain configuration

Configuration Example

plugins:
  enabled: true
  chain:
    - name: cors
      config:
        allowed_origins: ["*"]
        allowed_methods: ["GET", "POST", "PUT", "DELETE"]
        allowed_headers: ["Content-Type", "Authorization"]
        max_age: 3600

Acceptance Criteria

• CORS plugin implementation with config support
• Unit tests for CORS functionality
• Documentation in README
• Example configuration in helios.yaml

References

• https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
• Existing plugin examples: internal/plugins/logging/

[drakeRAGE]

Hey @0xReLogic , I want to contribute to this issue? Can u assign it to me?

[0xReLogic]

Hey @drakeRAGE

Thanks for your interest I'm assigning this issue to you.

Quick Brief

File location: internal/plugins/cors.go (single file, not a subdirectory)

Implementation pattern:

• Follow the same pattern as internal/plugins/logging.go and internal/plugins/headers.go
• Package: package plugins
• Register with RegisterBuiltin("cors", ...) in init() function
• Factory function receives cfg map[string]interface{} for configuration

Key CORS headers to set:

• Access-Control-Allow-Origin
• Access-Control-Allow-Methods
• Access-Control-Allow-Headers
• Access-Control-Max-Age
• Access-Control-Allow-Credentials (if needed)

Handle preflight:

• Check if request method is OPTIONS
• If yes, set CORS headers and return 204 No Content
• If no, set CORS headers and pass to next handler

Testing:

• Unit tests in internal/plugins/cors_test.go
• Test preflight OPTIONS requests
• Test actual requests with CORS headers
• Test origin matching (wildcard vs specific origins)

Important Reminders

1. Before pushing:

   • Run go fmt ./...
   • Run golangci-lint run
   • Run go test ./...
   • See CONTRIBUTING.md for pre-push checklist

2. When opening PR:

   • Tag this issue in PR description: Fixes #24 or Closes #24
   • This will auto-close the issue when PR is merged
   • Add clear description of what you implemented

3. Reference files:

   • internal/plugins/logging.go - good pattern for middleware
   • internal/plugins/headers.go - shows header manipulation
   • internal/plugins/registry.go - plugin registration

Let me know if you have any questions!