[ERC7598] コントラクトによる署名に対応したメタトランザクションの仕組みを理解しよう！

/**
 * @notice Execute a transfer with a signed authorization
 * @param from          Payer's address (Authorizer)
 * @param to            Payee's address
 * @param value         Amount to be transferred
 * @param validAfter    The time after which this is valid (unix time)
 * @param validBefore   The time before which this is valid (unix time)
 * @param nonce         Unique nonce
 * @param signature     Unstructured bytes signature signed by an EOA wallet or a contract wallet
 */
function transferWithAuthorization(
    address from,
    address to,
    uint256 value,
    uint256 validAfter,
    uint256 validBefore,
    bytes32 nonce,
    bytes memory signature
) external;

/**
 * @notice Receive a transfer with a signed authorization from the payer
 * @dev This has an additional check to ensure that the payee's address matches
 * the caller of this function to prevent front-running attacks. (See security
 * considerations)
 * @param from          Payer's address (Authorizer)
 * @param to            Payee's address
 * @param value         Amount to be transferred
 * @param validAfter    The time after which this is valid (unix time)
 * @param validBefore   The time before which this is valid (unix time)
 * @param nonce         Unique nonce
 * @param signature     Unstructured bytes signature signed by an EOA wallet or a contract wallet
 */
function receiveWithAuthorization(
    address from,
    address to,
    uint256 value,
    uint256 validAfter,
    uint256 validBefore,
    bytes32 nonce,
    bytes memory signature
) external;

/**
 * @notice Attempt to cancel an authorization
 * @param authorizer    Authorizer's address
 * @param nonce         Nonce of the authorization
 * @param signature     Unstructured bytes signature signed by an EOA wallet or a contract wallet
 */
function cancelAuthorization(
    address authorizer,
    bytes32 nonce,
    bytes memory signature
) external;

function transferWithAuthorization(
    address from,
    address to,
    uint256 value,
    uint256 validAfter,
    uint256 validBefore,
    bytes32 nonce,
    uint8 v,
    bytes32 r,
    bytes32 s
) external {
    transferWithAuthorization(
        from,
        to,
        value,
        validAfter,
        validBefore,
        nonce,
        abi.encodePacked(r, s, v)
    );
}

/**
  * @notice Execute a transfer with a signed authorization
  * @dev EOA wallet signatures should be packed in the order of r, s, v.
  * @param from          Payer's address (Authorizer)
  * @param to            Payee's address
  * @param value         Amount to be transferred
  * @param validAfter    The time after which this is valid (unix time)
  * @param validBefore   The time before which this is valid (unix time)
  * @param nonce         Unique nonce
  * @param signature     Signature byte array produced by an EOA wallet or a contract wallet
  */
function _transferWithAuthorization(
    address from,
    address to,
    uint256 value,
    uint256 validAfter,
    uint256 validBefore,
    bytes32 nonce,
    bytes memory signature
) internal {
    require(now > validAfter, "Authorization is not yet valid");
    require(now < validBefore, "Authorization is expired");
    require(!_authorizationStates[authorizer][nonce], "Authorization is used or canceled");

    bytes32 digest = keccak256(abi.encodePacked(
        hex"1901",
        DOMAIN_SEPARATOR,
        keccak256(abi.encode(
            TRANSFER_WITH_AUTHORIZATION_TYPEHASH,
            from,
            to,
            value,
            validAfter,
            validBefore,
            nonce
        ))
    ));
    require(
        // Check for both ECDSA signature and and ERC-1271 signature. A sample SignatureChecker is available at
        // https://github.com/OpenZeppelin/openzeppelin-contracts/blob/7bd2b2a/contracts/utils/cryptography/SignatureChecker.sol
        SignatureChecker.isValidSignatureNow(
            owner,
            typedDataHash,
            signature
        ),
        "Invalid signature"
    );

    _authorizationStates[authorizer][nonce] = true;
    emit AuthorizationUsed(authorizer, nonce);
    
    _transfer(from, to, value);
}

contract ContractWallet {
    function isValidSignature(bytes32 hash, bytes memory signature) public view returns (bool) {
        // カスタム署名検証ロジック
        // 例：ECDSAで署名を検証する
        address signer = ECDSA.recover(hash, signature);
        return signer == owner;
    }
}