Flutter - Android 7 CERTIFICATE_VERIFY_FAILED with LetsEncrypt SSL cert after Sept 30, 2021

After Sept 30, 2021, https get/post requests to a website using a Let’s Encrypt SSL certificate on an old Android 7 device were failing with this error: HandshakeException: Handshake error in client (OS Error: CERTIFICATE_VERIFY_FAILED: certificate has expired(handshake.cc:354))

Solution

In Flutter, to once again make SSL https connections on older devices to Let’s Encrypt SSL protected websites, we can supply Let’s Encrypt’s trusted certificate via SecurityContext to dart:io HttpClient object (from the dart native communications library), which we can use directly to make https get/post calls, or we can supply that customized HttpClient to Flutter/Dart package:http IOClient if we are using that popular pub.dev package.

Example

Here’s a Flutter unit test which creates a dart:io HttpClient with a SecurityContext that has a Let's Encrypt root certificate supplied to it. Then, this HttpClient is provided to package:http IOClient which implement's the Client interface and can be used for all the usual get, post etc. calls.

import 'dart:convert';
import 'dart:typed_data';
import 'dart:io';
import 'package:test/test.dart';
import 'package:http/http.dart' as http;
import 'package:http/io_client.dart';
void main() {
  const sslUrl = 'https://valid-isrgrootx1.letsencrypt.org/';