Getting platform specific data?

When using individual store plugins for IAPs we have access to data not accessible via Unity IAP. How do we get this if we switch to Unity IAP?

E.g.
On Google V2 we get an object of type GooglePurchase after a successful purchase. This object has fields named signature and originalJson which we send to AppsFlyer for receipt validation.

 

This may help http://answers.unity3d.com/questions/1191677/getting-unity-iap-receipt-data-to-validate-with-pl.html . Always a good idea to Search Google and Unity Answers.

 

Why not have this as part of the extensions functionality?

e.g.

var signature = extensions.GetExtension<IGoogleExtensions>().GetSignature(receipt);