Flutter webview intercept and add headers to all requests

In Flutter, if you want to intercept requests within a WebView and add headers to all requests, you can typically achieve this using the webview_flutter plugin. This plugin provides a WebView widget that enables Flutter applications to embed web content and handle request interception and processing through the navigationDelegate. Below, I will detail how to implement this.

Step 1: Add Dependencies

First, ensure your pubspec.yaml file includes the webview_flutter plugin:

yaml
dependencies:
  webview_flutter: ^2.0.4

Run flutter pub get to install the dependency.

Step 2: Use WebView Widget

In your Flutter application, you can use the WebView widget and provide a navigationDelegate function to intercept all network requests. Within this function, inspect the request URL and implement custom logic to decide whether to modify request headers or block the request.

dart
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

class MyWebView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: WebView(
        initialUrl: 'https://www.example.com',
        navigationDelegate: (NavigationRequest request) {
          if (request.url.startsWith('https://www.example.com')) {
            // Implement further processing, such as adding custom request headers
            // Directly modifying request headers is not feasible; instead, use a server or local proxy to modify requests
            return NavigationDecision.navigate;
          }
          return NavigationDecision.prevent; // Block loading for other URLs
        },
      ),
    );
  }
}

Step 3: Modify Request Headers

Since the WebView widget itself does not support directly modifying request headers, you need to employ alternative strategies, such as setting up a proxy server to modify headers on the proxy or operating at a higher network level.

If your application scenario requires adding request headers directly on the client side, consider exploring third-party libraries that support this feature or adjusting your application architecture to handle these operations on the server side.

Example

Suppose you have a service that requires adding an API key as a request header to all requests. If handling this on the client side is not feasible, modify the server configuration to automatically add the required API key header to requests or reconsider implementing proxy forwarding for client requests.

Conclusion

In the current implementation of webview_flutter, directly modifying request headers on the client side may not be the most straightforward approach. Considering server-side proxies or other network-level solutions may be more effective. However, with the development of the Flutter ecosystem, there may be more plugins or methods in the future that directly support this feature.