Implement revocation via smart contract

It is possible to implement Revocation using Conditions that rely on a function call to a Custom Smart Contract. This allows the handling of revocation to be decentralized and transparent. Here is an example of a smart contract (not suitable for production):

pragma solidity 0.8.7;

contract Revocation {

    mapping(address => bool) public isRevoked;

    function revoke(address user) public {
        isRevoked[user] = true;
    }

    function unRevoke(address user) public {
        isRevoked[user] = false;
    }
}

And the associated Condition:

const revocationCondition = {
  contractAddress: '<DEPLOYED_CONTRACT_ADDRESS>',
  method: 'isRevoked',
  parameters: [':userAddress'],
  functionAbi: {
    inputs: [
      {
        internalType: 'address',
        name: '',
        type: 'address',
      },
    ],
    name: 'isRevoked',
    outputs: [
      {
        internalType: 'bool',
        name: '',
        type: 'bool',
      },
    ],
    stateMutability: 'view',
    type: 'function',
  },
  chain: 1,
  returnValueTest: {
    comparator: '==',
    value: false,
  },
};

The condition we have defined calls the isRevoked function of the smart contract and passes the user's address. If the call returns false (not revoked, i.e. granted), then the TACo operation will occur. If the call returns true (is revoked), then TACo operation will fail.