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

pragma solidity ^0.4.24;

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() public {
    signers.add(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 {
    signers.add(account);
    emit SignerAdded(account);
  }

  function renounceSigner() public {
    signers.remove(msg.sender);
  }

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