Protect custom backend resources with App Check in Flutter projects

You can use App Check to protect non-Google custom backend resources for your app, like your own self-hosted backend. To do so, you'll need to do both of the following:

• Modify your app client to send an App Check token along with each request to your backend, as described on this page.
• Modify your backend to require a valid App Check token with every request, as described in Verify App Check tokens from a custom backend.

Before you begin

Add App Check to your app, using the default providers.

Send App Check tokens with backend requests

To ensure your backend requests include a valid, unexpired, App Check token, precede each request with a call to getToken(). The App Check library will refresh the token if necessary.

Once you have a valid token, send it along with the request to your backend. The specifics of how you accomplish this are up to you, but don't send App Check tokens as part of URLs, including in query parameters, as this makes them vulnerable to accidental leakage and interception. The recommended approach is to send the token in a custom HTTP header.

For example:

void callApiExample() async {
    final appCheckToken = await FirebaseAppCheck.instance.getToken();
    if (appCheckToken != null) {
        final response = await http.get(
            Uri.parse("https://yourbackend.example.com/yourExampleEndpoint"),
            headers: {"X-Firebase-AppCheck": appCheckToken},
        );
    } else {
        // Error: couldn't get an App Check token.
    }
}