EsiResponseCacheStrategyInterface implementations know how to compute the Response cache HTTP header based on the different ESI response cache headers.
This method can be implemented by domain objects which you want to store ACLs for if they do not have a getId() method, or getId() does not return a unique identifier.
This interface provides an additional level of indirection, so that we can work with abstracted versions of security objects and do not have to save the entire objects.