# Use tokens (/en/realtime-media/video/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 [#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 [#prerequisites]

Before starting, ensure that you have:

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

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

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

## Implement basic authentication [#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 [#use-a-token-to-join-a-channel-2]

    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 [#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 [#api-reference-5]

    * [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)