DonationControlledAccessWeb3.js

// Addresses
var contractAddress = "0xContractAddress";
var userAddress = "0xUserAddress";

// Message to sign : contract address + address to give access
var message = web3.sha3(contractAddress.substr(2) + userAddress.substr(2), {encoding: 'hex'})

// Signing message (with "\x19Ethereum Signed Message:\n32" as prefix by default)
web3.personal.sign(message, web3.eth.defaultAccount, (err, res) => sign = res)

//Extracting ECDSA variables
var r = sign.substr(0, 66);
var s = '0x' + sign.substr(66, 64);
var v = '0x' + sign.substr(130,2);