connect with backend

lib/services/token_interceptor.dart

@@ -0,0 +1,37 @@
+import 'package:dio/dio.dart';
+import 'package:flutter/material.dart';
+import '../providers/auth_provider.dart';
+
+class TokenInterceptor extends Interceptor {
+  final AuthProvider auth;
+  final BuildContext context;
+  final Dio dio;
+
+  TokenInterceptor(this.auth, this.context, this.dio);
+
+  @override
+  void onRequest(RequestOptions options, RequestInterceptorHandler handler) {
+    if (auth.token != null) {
+      options.headers['Authorization'] = 'Bearer ${auth.token}';
+    }
+    handler.next(options);
+  }
+
+  @override
+  void onError(DioException err, ErrorInterceptorHandler handler) async {
+    if (err.response?.statusCode == 401 &&
+        err.response?.data['message'] == 'Token has expired') {
+
+      final refreshed = await auth.tryRefreshToken(context);
+
+      if (refreshed) {
+        err.requestOptions.headers['Authorization'] = 'Bearer ${auth.token}';
+        final newResponse = await dio.fetch(err.requestOptions);
+        return handler.resolve(newResponse);
+      }
+    }
+
+    handler.next(err);
+  }
+}
+