Add revoke token when logging out

lib/api/twitch_api.dart

@@ -161,6 +161,20 @@ class TwitchApi {
     }
   }
 
+  /// Revokes the given [token] and returns a bool indicating success.
+  Future<bool> revokeToken({required String token}) async {
+    final url = Uri.parse('https://id.twitch.tv/oauth2/revoke');
+
+    final response = await _client.post(url, body: {'client_id': clientId, 'token': token});
+    if (response.statusCode == 200) {
+      debugPrint('Token revoked!');
+      return true;
+    } else {
+      debugPrint('Failed to revoke token :(');
+      return false;
+    }
+  }
+
   /// Returns a [StreamsTwitch] object that contains the top 20 streams and a cursor for further requests.
   Future<StreamsTwitch> getTopStreams({
     required Map<String, String> headers,

lib/core/auth/auth_store.dart

@@ -132,7 +132,8 @@ abstract class _AuthBase with Store {
   @action
   Future<void> logout() async {
     try {
-      // Delete the existing user token.
+      // Revoke the existing user token and delete it.
+      await twitchApi.revokeToken(token: _token!);
       await _storage.delete(key: 'USER_TOKEN');
       _token = null;
 
@@ -159,12 +160,12 @@ abstract class _AuthBase with Store {
           _tokenIsValid = await twitchApi.validateToken(token: _token!);
         }
       }
+      // Set the login status to logged out.
+      _isLoggedIn = false;
+
+      debugPrint('Successfully logged out');
     } catch (e) {
       debugPrint(e.toString());
     }
-    // Set the login status to logged out.
-    _isLoggedIn = false;
-
-    debugPrint('Successfully logged out');
   }
 }