s3api CORS support for web-based access

[Raphaël Droz]

I've CORS-permissive object container on Swift ("Access-Control-Allow-Origin" meta to "*").

I'd like to use a web-based file explorer for my bucket and since there is no such software over Swift/keystone v3 I looked at the S3 option: https://github.com/awslabs/aws-js-s3-explorer

After a few tweaks it seems like it could work but, as any web-based application, it issues "OPTIONS" preflight requests. Sadly, the s3 layer keeps responding "Bad URL" to OPTIONS blocking subsequent XHR coming from the app'.