Custom session key prefix for Session CacheStore

The current implementation allows no configuration and sets the cache key within a namespace: “_session_id:#{sid}”. The set CacheStore can use an additional namespace though.

https://github.com/rails/rails/blob/930110b0452bd33e0ee54e9ec6d68e904ba7a0ad/actionpack/lib/action_dispatch/middleware/session/cache_store.rb#L45

Anyone have any input on allowing a custom key like other session stores (dalli, redis-actionpack) or is there a specific reason why it has to be namespaced “_session_id”?