Approov Quickstart: Android Kotlin Retrofit

This quickstart is written specifically for native Android apps that are written in Kotlin and use Retrofit for making the API calls that you wish to protect with Approov. If this is not your situation then check if there is a more relevant Quickstart guide available.

This page provides all the steps for integrating Approov into your app. Additionally, a step-by-step tutorial guide using our Shapes App Example is also available.

To follow this guide you should have received an onboarding email for a trial or paid Approov account.

ADDING APPROOV SERVICE DEPENDENCY

The Approov integration is available via jitpack. This allows inclusion into the project by simply specifying a dependency in the gradle files for the app.

Firstly, jitpack needs to be added to the end the repositories section in the build.gradle file at the top root level of the project:

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

Secondly, add the dependency in your app's build.gradle:

dependencies {
	implementation 'com.github.approov:approov-service-retrofit:3.2.2'
}

Make sure you do a Gradle sync (by selecting Sync Now in the banner at the top of the modified .gradle file) after making these changes.

This package is actually an open source wrapper layer that allows you to easily use Approov with Retrofit. This has a further dependency to the closed source Approov SDK.

Make sure you do a Gradle sync (by selecting Sync Now in the banner at the top of the modified .gradle file) after making these changes.

MANIFEST CHANGES

The following app permissions need to be available in the manifest to use Approov:

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

Note that the minimum SDK version you can use with the Approov package is 21 (Android 5.0).

Please read this section of the reference documentation if targeting Android 11 (API level 30) or above.

INITIALIZING APPROOV SERVICE

In order to use the ApproovService you must initialize it when your app is created, usually in the onCreate method:

import io.approov.service.retrofit.ApproovService

class YourApp: Application() {
    override fun onCreate() {
        super.onCreate()
        ApproovService.initialize(applicationContext, "<enter-your-config-string-here>")
    }
}

The <enter-your-config-string-here> is a custom string that configures your Approov account access. This will have been provided in your Approov onboarding email.

USING APPROOV SERVICE

You can then modify your code that obtains a RetrofitInstance to make API calls as follows:

object ClientInstance {
    private static final String BASE_URL = "https://your.domain"
    private var retrofitBuilder: Retrofit.Builder? = null
    val retrofitInstance: Retrofit
        get() {
            if (retrofitBuilder == null) {
                retrofitBuilder = Retrofit.Builder()
                        .baseUrl(BASE_URL)
                        .addConverterFactory(GsonConverterFactory.create())
            }
            return ApproovService.getRetrofit(retrofitBuilder!!)
        }
}

This obtains a retrofit instance includes an OkHttp interceptor that protects channel integrity (with either pinning or managed trust roots). The interceptor may also add Approov-Token or substitute app secret values, depending upon your integration choices. You should thus use this client for all API calls you may wish to protect.

Approov errors will generate an ApproovException, which is a type of IOException. This may be further specialized into an ApproovNetworkException, indicating an issue with networking that should provide an option for a user initiated retry (which must make the new request with a call to the getRetrofit to get the latest client).

CUSTOM OKHTTP BUILDER

By default, the Retrofit instance gets a default client constructed with a default OkHttpClient. However, your existing code may use a customized OkHttpClient with, for instance, different timeouts or other interceptors. For example, if you have existing code:

val client = OkHttpClient.Builder().connectTimeout(5, TimeUnit.SECONDS).build()
val retrofit = retrofit2.Retrofit.Builder().baseUrl("https://your.domain/").client(client).build()

Pass the modified OkHttp.Builder to the ApproovService as follows:

ApproovService.setOkHttpClientBuilder(OkHttpClient.Builder().connectTimeout(5, TimeUnit.SECONDS))
val retrofitBuilder = retrofit2.Retrofit.Builder().baseUrl("https://your.domain/")
val retrofit = ApproovService.getRetrofit(retrofitBuilder)

This call to setOkHttpClientBuilder only needs to be made once. Subsequent calls to ApproovService.getRetrofit() will then always a OkHttpClient with the builder values included.

CHECKING IT WORKS

Initially you won't have set which API domains to protect, so the interceptor will not add anything. It will have called Approov though and made contact with the Approov cloud service. You will see logging from Approov saying UNKNOWN_URL.

Your Approov onboarding email should contain a link allowing you to access Live Metrics Graphs. After you've run your app with Approov integration you should be able to see the results in the live metrics within a minute or so. At this stage you could even release your app to get details of your app population and the attributes of the devices they are running upon.

NEXT STEPS

To actually protect your APIs and/or secrets there are some further steps. Approov provides two different options for protection:

• API PROTECTION: You should use this if you control the backend API(s) being protected and are able to modify them to ensure that a valid Approov token is being passed by the app. An Approov Token is short lived crytographically signed JWT proving the authenticity of the call.

• SECRETS PROTECTION: This allows app secrets, including API keys for 3rd party services, to be protected so that they no longer need to be included in the released app code. These secrets are only made available to valid apps at runtime.

Note that it is possible to use both approaches side-by-side in the same app.

See REFERENCE for a complete list of all of the ApproovService methods.