Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Storage class in an important concept in many commercial object stores. Using storage classes can generate important savings.

Describe the solution you'd like

A uniform way to set storage class on put that works on AWS, GCS, etc. It can be ignored if the object store doesn't support storage classes.

Describe alternatives you've considered

Attributes is a fixed list of names that doesn't include storage class. I suppose the HTTP client could be configured to add the extra header, but that breaks the abstraction completely.