• BC Break: Downgraded CorsListener priority from 250 to 28, this should not affect anyone but could be a source in case of strange bugs
• BC Break: Removed support for Symfony <4.3
• BC Break: Removed support for PHP <7.1
• Added support for Symfony 5
• Added support for configuration via env vars
• Changed the code to avoid mutating the EventDispatcher at runtime
• Changed the code to avoid returning Access-Control-Allow-Origin: null headers to mark blocked requests