openzeppelin-contracts/contracts/access/roles/SignerRole.sol

pragma solidity ^0.5.7;

import "../Roles.sol";

contract SignerRole {
    using Roles for Roles.Role;

    event SignerAdded(address indexed account);
    event SignerRemoved(address indexed account);

    Roles.Role private _signers;

    constructor () internal {
        _addSigner(msg.sender);
    }

    modifier onlySigner() {
        require(isSigner(msg.sender));
        _;
    }

    function isSigner(address account) public view returns (bool) {
        return _signers.has(account);
    }

    function addSigner(address account) public onlySigner {
        _addSigner(account);
    }

    function renounceSigner() public {
        _removeSigner(msg.sender);
    }

    function _addSigner(address account) internal {
        _signers.add(account);
        emit SignerAdded(account);
    }

    function _removeSigner(address account) internal {
        _signers.remove(account);
        emit SignerRemoved(account);
    }
}