The API to enable HSTS store is hiding this store's implementation/details: you only have to set a dir where we store HSTS policies. While this gives us some freedom (the store's format/logic could change at any time and QNAM is free to do whatever it likes with HSTS store), there is a serious flaw/drawback: several QNAM objects running in the same/different apps can access the same store concurrently. Thus the store's logic must be updated to deal with concurrent accesses properly.