Add ERC20 Permit (EIP-2612) (#2237)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
Co-authored-by: Santiago Palladino <spalladino@gmail.com>

test/helpers/eip712.js

@@ -0,0 +1,21 @@
+const ethSigUtil = require('eth-sig-util');
+
+const EIP712Domain = [
+  { name: 'name', type: 'string' },
+  { name: 'version', type: 'string' },
+  { name: 'chainId', type: 'uint256' },
+  { name: 'verifyingContract', type: 'address' },
+];
+
+async function domainSeparator (name, version, chainId, verifyingContract) {
+  return '0x' + ethSigUtil.TypedDataUtils.hashStruct(
+    'EIP712Domain',
+    { name, version, chainId, verifyingContract },
+    { EIP712Domain },
+  ).toString('hex');
+}
+
+module.exports = {
+  EIP712Domain,
+  domainSeparator,
+};