This is a Symfony bundle that adds Cross-Origin Resource Sharing (CORS) headers to HTTP responses and handles CORS preflight OPTIONS requests. It intercepts kernel request and response events, applies configurable per-URL rules (origin matching, allowed methods/headers, credentials, private network access, forced origin values, etc.), and automatically adds a `Vary: Origin` header to cacheable responses. The bundle is well-structured with a clean provider/resolver pattern for configuration, supports Symfony 5.4 through 8.0 and PHP 7.2+, and includes full CI and static analysis. It is a mature, actively maintained library that solves a specific HTTP security concern in a robust and extensible manner.