Abstract
An EIP-5792 compliant capability that allows wallets to indicate to apps that they have access to funds beyond those that can be accounted for by looking up balances onchain given the wallet’s address.
Motivation
Many applications check users’ balances before letting them complete some action. For example, if a user wants to swap some amount of tokens on a dex, the dex will commonly block the user from doing so if it sees that the user does not have that amount of tokens at their address. However, more advanced wallets have features that let users access funds from other sources. Wallets need a way to tell apps that they have access to additional funds so that users using these more advanced wallets are not blocked by balance checks.
Specification
One new EIP-5792 wallet capability is defined.
Wallet Implementation
To conform to this specification, wallets that wish to indicate that they have access to auxiliary funds MUST respond to wallet_getCapabilities calls with an auxiliaryFunds object with a supported field set to true for each chain they have access to auxiliary funds on. This specification does not put any constraints on the source of the auxiliary funds.
wallet_getCapabilities Response Specification
type AuxiliaryFundsCapability = {
supported: boolean;
}
wallet_getCapabilities Example Response
{
"0x2105": {
"auxiliaryFunds": {
"supported": true
},
},
"0x14A34": {
"auxiliaryFunds": {
"supported": true
}
}
}
App Implementation
When an app sees that a connected wallet has access to auxiliary funds via the auxiliaryFunds capability in a wallet_getCapabilities response, the app SHOULD NOT block users from taking actions on the basis of asset balance checks.
Rationale
Alternatives
Advanced Balance Fetching
An alternative we considered is defining a way for apps to fetch available auxiliary balances. This could be done, for example, by providing a URL as part of the auxiliaryFunds capability that apps could use to fetch auxiliary balance information. However, we ultimately decided that a boolean was enough to indicate to apps that they should not block user actions on the basis of balance checks, and it is minimally burdensome for apps to implement.
The shape of this capability allows for a more advanced extension if apps feel more functionality is needed.
Auxiliary Funds per Asset
We could also specify auxiliary funds support per asset. We decided against this because this list could get quite large if a wallet has auxiliary funds supports for many assets, and a single boolean should be enough for apps to not block users from taking actions.
Security Considerations
Apps MUST NOT make any assumptions about the source of auxiliary funds. Apps’ smart contracts SHOULD still, as they would today, make appropriate balance checks onchain when processing a transaction.