Retrieve bearer token postman to flutter

I've created a simple login feature on my flutter project and it works by inputting just an email and a password, and now I want to add the token bearer feature from postman so that users can still log in even though the application has been closed. What I want to ask is how do I get the token bearer value into shared preferences function?

This is my login code:

login() async {
final response = await http.post(
  "https://api.batulima.com//v1_ships/login_app",
  body: {"email": email, "password": password},
);
final data = jsonDecode(response.body);
String status = data['status'];
String message = data['message'];
if (status == "success") {
  Navigator.of(context).pushReplacement(PageRouteBuilder(
      pageBuilder: (_, __, ___) => new bottomNavBar(),
      transitionDuration: Duration(milliseconds: 600),
      transitionsBuilder:
          (_, Animation<double> animation, __, Widget child) {
        return Opacity(
          opacity: animation.value,
          child: child,
        );
      }));
  print(message);
} else {
  print(message);
 }
}

and this is my postman JSON structure:

{
"status": "success",
"data": {
    "apikey": "ak5neGVDd3h4M0lVeVF2b2hXWjg3OEZMYUlvcWExTXRqQ21xSmJGWQ==",
    "id_user": 49,
    "id_role": "8",
    "name_role": "Ship Owner",
    "email": "afriansyahm86@gmail.com",
    "phone": "082258785595",
    "saldo": "0",
    "photo": "https://batulimee.com/foto_user/avatar.png"
},
"message": "login successfully "
}

What should I add to be able to retrieve the value from apikey?

Below is the getpref that I have created in main.dart. if its null, its start from the splash screen to the login page. and if the apikey has been saved, its going to bottomnavbar page

Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
SharedPreferences prefs = await SharedPreferences.getInstance();
var apikey = prefs.getString('apikey');
print(apikey);
runApp(MaterialApp(
  debugShowCheckedModeBanner: false,
  home: apikey == null ? splash() : bottomNavBar()));
}

You can copy paste run full code below
To retrieve the value of apikey in JSON you can do data['data']['apikey']
code snippet

String apiKey = data['data']['apikey'];
print("apiKey $apiKey");

SharedPreferences prefs = await SharedPreferences.getInstance();   
await prefs.setString('apiKey', apiKey);

String getedApiKey = await prefs.getString('apiKey');
print(getedApiKey);

output

I/flutter (22942): apiKey ak5neGVDd3h4M0lVeVF2b2hXWjg3OEZMYUlvcWExTXRqQ21xSmJGWQ==
I/flutter (22942): ak5neGVDd3h4M0lVeVF2b2hXWjg3OEZMYUlvcWExTXRqQ21xSmJGWQ==
I/flutter (22942): login successfully 

full code

import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  login() async {
    /*final response = await http.post(
      "https://api.batulima.com//v1_ships/login_app",
      body: {"email": email, "password": password},
    );*/
    String jsonString = '''
    {
"status": "success",
"data": {
    "apikey": "ak5neGVDd3h4M0lVeVF2b2hXWjg3OEZMYUlvcWExTXRqQ21xSmJGWQ==",
    "id_user": 49,
    "id_role": "8",
    "name_role": "Ship Owner",
    "email": "afriansyahm86@gmail.com",
    "phone": "082258785595",
    "saldo": "0",
    "photo": "https://batulimee.com/foto_user/avatar.png"
},
"message": "login successfully "
}
    ''';
    final response = http.Response(jsonString, 200);

    final data = jsonDecode(response.body);
    String status = data['status'];
    String message = data['message'];
    String apiKey = data['data']['apikey'];
    print("apiKey $apiKey");

    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('apiKey', apiKey);

    String getedApiKey = await prefs.getString('apiKey');
    print(getedApiKey);

    if (status == "success") {
      /* Navigator.of(context).pushReplacement(PageRouteBuilder(
          pageBuilder: (_, __, ___) => new bottomNavBar(),
          transitionDuration: Duration(milliseconds: 600),
          transitionsBuilder:
              (_, Animation<double> animation, __, Widget child) {
            return Opacity(
              opacity: animation.value,
              child: child,
            );
          }));*/
      print(message);
    } else {
      print(message);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: login,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}