How to solve Flutter CERTIFICATE_VERIFY_FAILED error while performing a POST request?

I am sending a post request in Dart. It is giving a response when I test it on API testing tools such as Postman. But when I run the app. It gives me the following error:-

E/flutter ( 6264): HandshakeException: Handshake error in client (OS Error: E/flutter ( 6264):  CERTIFICATE_VERIFY_FAILED: unable to get local issuer certificate(handshake.cc:363))

Here is my code of the function -

Future getAccessToken(String url) async {

    try {
      http.post('url',
          body: {
            "email": "xyz@xyz.example",
            "password": "1234"
          }).then((response) {
        print("Reponse status : ${response.statusCode}");
        print("Response body : ${response.body}");
        var myresponse = jsonDecode(response.body);
        String token = myresponse["token"];
      });
    } catch (e) {
      print(e.toString());
    }

Here's the full error body:

E/flutter ( 6264): [ERROR:flutter/shell/common/shell.cc(184)] Dart Error: Unhandled exception: E/flutter ( 6264): HandshakeException: Handshake error in client (OS Error: E/flutter ( 6264):   CERTIFICATE_VERIFY_FAILED: unable to get local issuer certificate(handshake.cc:363)) E/flutter ( 6264): #0      IOClient.send (package:http/src/io_client.dart:33:23) E/flutter ( 6264): <asynchronous suspension> E/flutter ( 6264): #1      BaseClient._sendUnstreamed (package:http/src/base_client.dart:169:38) E/flutter ( 6264): <asynchronous suspension> E/flutter ( 6264): #2     BaseClient.post (package:http/src/base_client.dart:54:7) E/flutter ( 6264): #3      post.<anonymous closure> (package:http/http.dart:70:16) E/flutter ( 6264): #4      _withClient (package:http/http.dart:166:20) E/flutter ( 6264): <asynchronous suspension> E/flutter ( 6264): #5     post (package:http/http.dart:69:5) E/flutter ( 6264): #6
_MyLoginFormState.getAccessToken (package:chart/main.dart:74:7) E/flutter ( 6264): <asynchronous suspension> E/flutter ( 6264): #7
_MyLoginFormState.build.<anonymous closure> (package:chart/main.dart:64:29)

Solution

In order to enable this option globally in your project, here is what you need to do:

In your main.dart file, add or import the following class:

 import 'dart:io';

 class MyHttpOverrides extends HttpOverrides{
  @override
  HttpClient createHttpClient(SecurityContext? context){
    return super.createHttpClient(context)
      ..badCertificateCallback = (X509Certificate cert, String host, int port)=> true;
  }
}

In your main function, add the following line after function definition:

 HttpOverrides.global = MyHttpOverrides();

Your main.dart should look like this

void main() {
 // Your code
 
 HttpOverrides.global = MyHttpOverrides();
  runApp(const ConsultationApp());
}

This comment was very helpful to pass through this matter, and please note that...

This should be used while in development mode, do NOT do this when you want to release to production, the aim of this answer is to make the development a bit easier for you, for production, you need to fix your certificate issue and use it properly, look at the other answers for this as it might be helpful for your case.