# Use tokens (/en/realtime-media/broadcast-streaming/build/authenticate-users/use-tokens/flutter)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

To protect your business, it is best practice to authenticate every client that joins a channel. This guide explains how to fetch an authentication token from your token server, use it to join a channel, and renew the token when it expires.

## Understand the tech

      
  
      
  
      
  
      
  
      
  
      
  
      
When a user attempts to connect to an Agora channel, your app retrieves a token from the token server in your security infrastructure. Your app then sends this token to Agora SDRTN® for authentication. Agora SDRTN® reads the information stored in the token to validate the request.

The following figure shows the call flow you implement to create step-up-authentication with Agora Broadcast Streaming:

**Token authentication flow**

![token authentication flow](https://assets-docs.agora.io/images/video-sdk/token-authentication.svg)

## Prerequisites

Before starting, ensure that you have:

* Implemented the [Quickstart](../../index) in your project.

* Deployed a token server using either of the following guides:

  * [Deploy a token server](deploy-token-server)
  * [Deploy a middleware server](middleware-token-server)

## Implement basic authentication

This section shows you how to implement basic authentication by acquiring a token and using it to join a channel.

### Use a token to join a channel

This section shows you how to integrate token authentication in your app.

1. Add the following to the `pubspec.yaml` file, under `dependencies`:

   ```yaml
   dependencies:
     # Agora Flutter SDK, use the latest version of agora_rtc_engine
     agora_rtc_engine: ^6.3.0
     # For making http requests
     http: ^0.13.5
   ```

2. Replace the contents in `/lib/main.dart` with the following code.

**Sample code for basic authentication**

```dart
  import 'dart:convert';

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

    void main() => runApp(const MyApp());

    /// This widget is the root of your application.
    class MyApp extends StatefulWidget {
    /// Construct the [MyApp]
    const MyApp({Key? key}) : super(key: key);

    @override
    State<MyApp> createState() => _MyAppState();
    }

    class _MyAppState extends State<MyApp> {

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('APIExample'),
        ),
        body: const JoinChannelVideoToken()),
      );
    }
    }

    class JoinChannelVideoToken extends StatefulWidget {
    const JoinChannelVideoToken({Key? key}) : super(key: key);

    @override
    State<StatefulWidget> createState() => _State();
    }

    class _State extends State<JoinChannelVideoToken> {
    late final RtcEngine _engine;
    bool _isReadyPreview = false;

    bool isJoined = false, switchCamera = true, switchRender = true;
    Set<int> remoteUid = {};
    static const String appId = '<Your app ID>'; // Fill in the information from Agora console
    static const String channelId = '<Your channel name>'; // Fill in the channel name
    static const String hostUrl = '<Your host URL and port>'; // Fill in the server URL and port

    @override
    void initState() {
      super.initState();
      _initEngine();
    }

    @override
    void dispose() {
      super.dispose();
      _dispose();
    }

    Future<void> _dispose() async {
      await _engine.leaveChannel();
      await _engine.release();
    }

    Future<void> _initEngine() async {
      _engine = createAgoraRtcEngine();
      await _engine.initialize(const RtcEngineContext(
      appId: appId,
      ));

      _engine.registerEventHandler(RtcEngineEventHandler(
      onJoinChannelSuccess: (RtcConnection connection, int elapsed) {
        setState(() {
        isJoined = true;
        });
      },
      onUserJoined: (RtcConnection connection, int rUid, int elapsed) {
        setState(() {
        remoteUid.add(rUid);
        });
      },
      onUserOffline:
        (RtcConnection connection, int rUid, UserOfflineReasonType reason) {
        setState(() {
        remoteUid.removeWhere((element) => element == rUid);
        });
      },
      onLeaveChannel: (RtcConnection connection, RtcStats stats) {
        setState(() {
        isJoined = false;
        remoteUid.clear();
        });
      },
      onTokenPrivilegeWillExpire: (RtcConnection connection, String token) {
        _fetchToken(1234, channelId, 1, false);
      },
      onRequestToken: (RtcConnection connection) {
        _fetchToken(1234, channelId, 1, true);
      },
      ));

      await _engine.enableVideo();

      await _engine.startPreview();
      await _fetchToken(1234, channelId, 1, true);

      setState(() {
      _isReadyPreview = true;
      });
    }

    Future<void> _fetchToken(
      int uid,
      String channelName,
      int toeknRole,
      bool needJoinChannel,
    ) async {
      var client = http.Client();
      try {
      Map<String, String> headers = {
        'Content-type': 'application/json',
        'Accept': 'application/json',
      };

      var response = await client.post(Uri.parse(hostUrl),
        headers: headers,
        body: jsonEncode(
          {'uid': uid, 'ChannelName': channelName, 'role': toeknRole}));
      var decodedResponse = jsonDecode(utf8.decode(response.bodyBytes)) as Map;

      final token = decodedResponse['token'];
      if (needJoinChannel) {
        await _engine.joinChannel(
        token: token,
        channelId: channelName,
        uid: uid,
        options: const ChannelMediaOptions(
          channelProfile: ChannelProfileType.channelProfileLiveBroadcasting,
          clientRoleType: ClientRoleType.clientRoleBroadcaster,
        ),
        );
      } else {
        await _engine.renewToken(token);
      }
      } finally {
      client.close();
      }
    }

    @override
    Widget build(BuildContext context) {
      if (!_isReadyPreview) return Container();
      return Stack(
      children: [
        AgoraVideoView(
        controller: VideoViewController(
          rtcEngine: _engine,
          canvas: const VideoCanvas(uid: 0),
        ),
        ),
        Align(
        alignment: Alignment.topLeft,
        child: SingleChildScrollView(
          scrollDirection: Axis.horizontal,
          child: Row(
          children: List.of(remoteUid.map(
            (e) => SizedBox(
            width: 120,
            height: 120,
            child: AgoraVideoView(
              controller: VideoViewController.remote(
              rtcEngine: _engine,
              canvas: VideoCanvas(uid: e),
              connection: const RtcConnection(channelId: channelId),
              ),
            ),
            ),
          )),
          ),
        ),
        )
      ],
      );
    }
    }
```

Replace `<Your app ID>` with your app ID, which must be consistent with the app ID you specified in the server configuration. Update `<Your host URL and port>` with the host URL and port of the local Golang server you have deployed. For example `99.9.9.99:8082`.

The sample code implements the following logic:

* Calls `joinChannel` to join a channel using the user ID, the channel name, and a token you obtain from the server. The user ID and channel name you specify must be consistent with the values you used to generate the token.

* The SDK triggers an `onTokenPrivilegeWillExpire` callback 30 seconds before the token expires. After receiving the callback, you obtain a new token from the server and call `renewToken` to pass the newly generated token to the SDK.

* If the token expires, the SDK triggers an `onRequestToken` callback. After receiving the callback, obtain a new token from the server and call `joinChannel` with the new token to rejoin the channel.

Build and run the project on the local device, the app performs the following operations:

* Obtains a token from your token server.
* Joins the channel.
* Automatically renews the token when it is about to expire.

<CalloutContainer type="info">
  <CalloutDescription>
    The user ID and channel name used to join a channel must be consistent with the values used to generate the token.
  </CalloutDescription>
</CalloutContainer>

## Reference

This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

### API reference

* [renewToken](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/class_irtcengine.html#api_irtcengine_renewtoken)

* [onTokenPrivilegeWillExpire](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_ontokenprivilegewillexpire)

* [onConnectionStateChanged](https://api-ref.agora.io/en/video-sdk/flutter/6.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onconnectionstatechanged)