# Use tokens (/en/realtime-media/interactive-live-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 [#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 Interactive Live Streaming:

    **Token authentication flow**

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

    ## Prerequisites [#prerequisites-6]

    Before starting, ensure that you have:

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

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

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

    ## Implement basic authentication [#implement-basic-authentication-6]

    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-6]

    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 [#reference-6]

    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)