[Flutter - Android] Sending POST request with JSON body using `InAppWebView` results in 415 Unsupported Media Type

[x] I have read the Getting Started section
[x] I have already searched for the same problem

Environment

Technology	Version
Flutter version	3.19.3
Plugin version	6.0.0
Android version
iOS version
macOS version
Xcode version
Google Chrome version

Device information:

All Android emulators
Samsung Galaxy A33 5G
Samsung Galaxy Tab A8

Description

In my Flutter app, I want my logged-in user to be able to click on a button that opens an internal browser to access a server requiring an authentication, and I want to pass the user's JWT auth token in the request to avoid the user to authenticate to that server. I have read the Getting Started section I have the following configurations:

minSdkVersion 21

<uses-permission android:name="android.permission.INTERNET"/>

<meta-data
android:name="flutterEmbedding"
android:value="2" />

I created my app in summer 2023, so I guess I do not need to worry about migrating to AndroidX (do I?)

Expected behavior: Using InAppWebView to open an internal browser, configuring the initialUrlRequest to send a POST request with a JSON content, I expect to have my request received by the server and successfully detected as having its Content-Type set to application/json.

Current behavior: When opening the InAppWebView, I get a page with a

415 Unsupported Media Type
Did not attempt to load JSON data because the request Content-Type was not 'application/json'.

The exact same code works for iOS (I get the expect web page), but not for Android (I get the 415)

Steps to reproduce

Have a simple button opening the preconfigured InAppWebView sending an initial POST request with a server expecting for the answer
Notice it works on iOS but not on Android

...
ElevatedButton(
   onPressed: () => Navigator.push(context,
      MaterialPageRoute(builder: (_) => const CustomInAppBrowser()),
   ),
   child: const Text('Open InAppWebView'),
)

class CustomInAppBrowser extends StatelessWidget {
  const CustomInAppBrowser({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: const Icon(Icons.close),
          onPressed: () {
            Navigator.of(context).pop();
          },
        ),
        title: const Text('InAppWebView'),
      ),
      body: InAppWebView(
        initialUrlRequest: URLRequest(
          url: WebUri('server_address_here/token'),
          method: 'POST',
          body: utf8.encode(
            jsonEncode({"token": jwtAuthTokenAsStringHere}),
          ),
          headers: {
            'Content-Type': 'application/json',
          },
        ),
        onWebViewCreated: (controller) {},
      ),
    );
  }
}

👋 @Cyrille-Dakhlia

NOTE: This comment is auto-generated.

Are you sure you have already searched for the same problem?

Some people open new issues but they didn't search for something similar or for the same issue. Please, search for it using the GitHub issue search box or on the official inappwebview.dev website, or, also, using Google, StackOverflow, etc. before posting a new one. You may already find an answer to your problem!

If this is really a new issue, then thank you for raising it. I will investigate it and get back to you as soon as possible. Please, make sure you have given me as much context as possible! Also, if you didn't already, post a code example that can replicate this issue.

In the meantime, you can already search for some possible solutions online! Because this plugin uses native WebView, you can search online for the same issue adding android WebView [MY ERROR HERE] or ios WKWebView [MY ERROR HERE] keywords.

Following these steps can save you, me, and other people a lot of time, thanks!

pichillilorenzo / flutter_inappwebview