Sponsored Fees

[Nana-EC]

Description:
This HIP proposes an expansion to the approval and allowance network logic (i.e. CryptoApproveAllowance, NftAllowance
and TokenAllowance) by allowing any account on the network to provide allowances that will sponsor the payment of the
fees for another account’s submitted transactions.
In this way account Alice may assign an HBAR / token transaction fee allowance for EOA account Bob or Contract account
Carol and pay the fees due to nodes, the network and accounts for any transactions they submit, thus allowing Bob or
Carol to have zero balance and still transact on chain.

This proposal extends the existing Approval and Allowance API by adding the concept of a scope that designates the type
of value transafer an allowance applies to.
The scopes will include CryptoTranafer, HAPI transsaction fee and token custom fees.
This enables value transfer and fee payments to another account without requiring one-off
approval for each transaction. This feature enhances flexibility and efficiency in managing transaction costs,
particularly for high volume applications.

Related issue(s):

Fixes #912

Notes for reviewer:
Expect more changes soon.
There's an outstanding item to condense the Allowances types to instead be scopes on the existing allowances as a cleaner API form

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

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[Nana-EC]

Updated HIP with scope concept and fixed PR description with updated Abstract

[tud0r6]

Would it be possible for sponsored fees to be optionally set towards spending by a smart contract, thus limiting the scope of the approval to executing only 1 particular smart contract.

[gregscullard]

Would it be possible for sponsored fees to be optionally set towards spending by a smart contract, thus limiting the scope of the approval to executing only 1 particular smart contract.

@tud0r6 I like this idea, to be clear, you mean that if I grant some hbar to Alice, I would be able to specify that Alice can only spend the hBar on executing transactions related to a specific contract, nothing else. She would not be able to execute another contract, or create an NFT, etc...

Note, hbar in this case is gas for contracts, does the allowance extend to paying for gas (through the SDK and/or relay), or just native fees ? If only native fees, we may need to consider supporting gas payments.

[Nana-EC]

Would it be possible for sponsored fees to be optionally set towards spending by a smart contract, thus limiting the scope of the approval to executing only 1 particular smart contract.

@tud0r6 I like this idea, to be clear, you mean that if I grant some hbar to Alice, I would be able to specify that Alice can only spend the hBar on executing transactions related to a specific contract, nothing else. She would not be able to execute another contract, or create an NFT, etc...

Note, hbar in this case is gas for contracts, does the allowance extend to paying for gas (through the SDK and/or relay), or just native fees ? If only native fees, we may need to consider supporting gas payments.

Great considerations @gregscullard and @tud0r6 .
So the intention of this HIP was to cover value transfers that cover fees.
Initially it was not intended for gas, however, gas is eventually settled used to define the work but it's paid in the form of hbar.
So there's a possibility to extend it to cover gas payments with a specific scope or as GAS_PAYMENT 🤔.
I like it, though we need to think on any unintended emergent features here 😅.
For example the Ethereum JSON RPC API doesn't support the ability for an EOA to specify the transaction is sponsored. Which would mean it might only be available via ContractCall/ContractCreate HAPI and not via EthereumTransaction

[tud0r6]

tention of this HIP was to cover value transfers that cover fees.
Initially it was not intended for gas, however, gas is eventually settled used to define the work but it's paid in the form of hbar.

Indeed, I won't want to sponsor general-use gas(HBAR), rather application(SC)-specific gas(HBAR).

[Nana-EC]

@gregscullard and @tud0r6 I've added the gas scope but also added thoughts in the open questions section around some challenges here.
Any ideas on how to address this?