# Use tokens (/en/realtime-media/rtc/build/authenticate-users/authentication-workflow/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 Video Calling:

<Accordions>
  <Accordion title="Token authentication flow">
    ![token authentication flow](https://assets-docs.agora.io/images/video-sdk/token-authentication.svg)
  </Accordion>
</Accordions>

## Prerequisites

Before starting, ensure that you have:

* Implemented the [Quickstart](/en/realtime-media/rtc/get-started-sdk) in your project.

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

  * [Deploy a token server](/en/realtime-media/rtc/build/authenticate-users/deploy-token-server)
  * [Deploy a middleware server](/en/realtime-media/rtc/build/authenticate-users/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.

   ```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="warning">
  <CalloutTitle>
    Note
  </CalloutTitle>

  <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)