withdraw function in socialLock.sol

SocialLock_withdraw.sol

  function withdraw(string memory headerJson, string memory payloadJson, bytes memory signature, uint amount) public {
    // validate JWT
    string memory email = validateJwt(headerJson, payloadJson, signature);
    bytes32 emailHash = keccak256(abi.encodePacked(email));
    
    // balance check
    // this uses the email address from the Google JWT to check if there is a balance for this email
    require(balances[emailHash] > 0, "No balance for this email");
    require(balances[emailHash] >= amount, "Not enough balance for this email");

    // transfer
    balances[emailHash] -= amount;
    msg.sender.transfer(amount);
  }