Validating in app purchase locally for non consumable in Flutter with official plugin

I am trying to validate locally in app purchase of non consumable in Flutter with their official plugin in_app_purchase.

I get localVerificationData string in verificationData in PurchaseDetails object. But I have no idea how to use this localVerification string in this verification process.

I found in this Apple doc saying that

Validating locally requires code to read and validate a PKCS #7 signature, and code to parse and validate the signed payload

But still I need help with code samples to do this in Flutter.