Get payload of JWT token in Dart language

jwt-payload-parse.dart

import 'dart:convert';

Map<String, dynamic> parseJwt(String token) {
  final parts = token.split('.');
  if (parts.length != 3) {
    throw Exception('invalid token');
  }

  final payload = _decodeBase64(parts[1]);
  final payloadMap = json.decode(payload);
  if (payloadMap is! Map<String, dynamic>) {
    throw Exception('invalid payload');
  }
  print(payloadMap);
  return payloadMap;
}

String _decodeBase64(String str) {
  String output = str.replaceAll('-', '+').replaceAll('_', '/');

  switch (output.length % 4) {
    case 0:
      break;
    case 2:
      output += '==';
      break;
    case 3:
      output += '=';
      break;
    default:
      throw Exception('Illegal base64url string!"');
  }

  return utf8.decode(base64Url.decode(output));
}

void main() {
  parseJwt(
      "eyJhbGciOiJIUzI1NiJ9.eyJ1c3VhcmlvX2xvZ2dlZCI6MSwiYWRtaW4iOnRydWUsImV4cCI6MTU0ODE3ODY2Nn0.lAzR0RkP1MXYjOwYkUkVJC2FFIgu7LwWjwB_uA6QSjw");
}