Flutter app: How to implement a proper logout function?

Question

I have a flutter App using Azure B2C authentication. To achieve this I use the flutter appAuth package. The login process works fine but appAuth does not provide a logout functionality. After logging in I get an access token. Until now my logout was to delete this access token.

The problem is, that Azure require a web app session lifetime of at least 15 minutes in the SignIn user flow. This means: If a user logs in and out within 15 minutes, he will automatically be logged in again. This makes a login with another user impossible.

I hope to fix this behavior with a real logout instead of only deleting the access tokens. In found the following line of code in the Azure Active Directory documentation. But I cannot manage to get it running. Any suggestions for a logout function?

GET https://{tenant}.b2clogin.com/{tenant}.onmicrosoft.com/{policy}/oauth2/v2.0/logout?post_logout_redirect_uri=https%3A%2F%2Fjwt.ms%2F

Solution

I followed the below source to implement the below log out function using app auth written by David White.

Future<void> _logOut() async {
    try {
      //for some reason the API works differently on iOS and Android
      Map<String, String> additionalParameters;
      if (Platform.isAndroid) {
        //works on Android but will miss p parameter when redirected back to authorize on iOS
        additionalParameters = {
          "id_token_hint": _idToken,
          "post_logout_redirect_uri": _redirectUrl
        };
      } else if (Platform.isIOS) {
        // with p parameter when redirected back to authorize on iOS
        additionalParameters = {
          "id_token_hint": _idToken,
          "post_logout_redirect_uri": _redirectUrl,
          'p': '<tenantID>'
        };
      }
      await appAuth.authorizeAndExchangeCode(
        AuthorizationTokenRequest(
          _clientId,
          _redirectUrl,
          promptValues: ['login'],
          discoveryUrl: _discoveryURL,
          additionalParameters: additionalParameters,
          scopes: _scopes,
        ),
      );
    } catch (e) {
      print(e);
    }
    setState(() {
      _jwt = null;
    });
  }

source: https://www.detroitdave.dev/2020/04/simple-azure-b2c-flutter.html