decodePayload function
Implementation
String decodePayload(String payloadBase64) {
var delta4 = payloadBase64.length % 4;
if (delta4 > 0 && delta4 < 4) {
payloadBase64 =
payloadBase64.padRight(payloadBase64.length + (4 - delta4), '=');
}
var json = utf8.decode(base64Decode(payloadBase64));
return json;
}