# 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.

**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="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)