You can protect your app's non-Firebase resources, such as self-hosted backends, with App Check. To do so, you will 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 either the default Play Integrity provider, or a custom provider.
Send App Check tokens with backend requests
To ensure your backend requests include a valid, unexpired, App Check token,
wrap each request in a call to getAppCheckToken()
. The App Check library
will refresh the token if necessary, and you can access the token in the
method's success listener.
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, if you use Retrofit:
Kotlin
class ApiWithAppCheckExample { interface YourExampleBackendService { @GET("yourExampleEndpoint") fun exampleData( @Header("X-Firebase-AppCheck") appCheckToken: String, ): Call<List<String>> } var yourExampleBackendService: YourExampleBackendService = Retrofit.Builder() .baseUrl("https://yourbackend.example.com/") .build() .create(YourExampleBackendService::class.java) fun callApiExample() { Firebase.appCheck.getAppCheckToken(false).addOnSuccessListener { appCheckToken -> val token = appCheckToken.token val apiCall = yourExampleBackendService.exampleData(token) // ... } } }
Java
public class ApiWithAppCheckExample { private interface YourExampleBackendService { @GET("yourExampleEndpoint") Call<List<String>> exampleData( @Header("X-Firebase-AppCheck") String appCheckToken); } YourExampleBackendService yourExampleBackendService = new Retrofit.Builder() .baseUrl("https://yourbackend.example.com/") .build() .create(YourExampleBackendService.class); public void callApiExample() { FirebaseAppCheck.getInstance() .getAppCheckToken(false) .addOnSuccessListener(new OnSuccessListener<AppCheckToken>() { @Override public void onSuccess(@NonNull AppCheckToken appCheckToken) { String token = appCheckToken.getToken(); Call<List<String>> apiCall = yourExampleBackendService.exampleData(token); // ... } }); } }
Replay protection (beta)
When making a request to an endpoint for which you've enabled
replay protection,
wrap the request in a call to getLimitedUseAppCheckToken()
instead of
getAppCheckToken()
:
Kotlin
Firebase.appCheck.limitedUseAppCheckToken.addOnSuccessListener { // ... }
Java
FirebaseAppCheck.getInstance() .getLimitedUseAppCheckToken().addOnSuccessListener( new OnSuccessListener<AppCheckToken>() { @Override public void onSuccess(AppCheckToken appCheckToken) { String token = appCheckToken.getToken(); // ... } } );