InstaContract/contracts/MoatAddress.sol

// Implement the proper governance mechanism to update the admin address like admin have rights to upgrade anything but not just "admin". Governance will be used to set admin address.
// Or keep AllowedResolver also in MoatAddress contract

pragma solidity ^0.4.24;

contract AddressRegistry {

    event AddressChanged(string name, address target);
    mapping(bytes32 => address) internal addressRegistry;

    modifier onlyAdmin() {
        require(
            msg.sender == getAddr("admin"),
            "Permission Denied"
        );
        _;
    }

    constructor() public {
        addressRegistry[keccak256("admin")] = msg.sender;
    }

    function setAddr(string name, address newAddress) public onlyAdmin {
        addressRegistry[keccak256(name)] = newAddress;
        emit AddressChanged(name, newAddress);
    }

    function getAddr(string name) public view returns(address addr) {
        addr = addressRegistry[keccak256(name)];
        require(addr != address(0), "Not a valid address.");
    }

    // Contract Address >> Asset Owner Address >> Bool
    mapping(address => mapping(address => bool)) allowedResolver;

    function allowContract() public {
        allowedResolver[getAddr("resolver")][msg.sender] = true;
    }

    function disallowContract() public {
        allowedResolver[getAddr("resolver")][msg.sender] = false;
    }

    function isApprovedResolver(address user) public view returns(bool) {
        return allowedResolver[getAddr("resolver")][user];
    }

}