SafetyNet Attestation Example Implementation for Validating Device Authenticity on Android

SafetyNetAttestation.kt

import android.content.Context
import android.util.Base64
import com.google.android.gms.safetynet.SafetyNet
import inject.AppContext
import inject.modules.GoogleServicesModule.GoogleContext
import io.reactivex.Single
import java.io.ByteArrayOutputStream
import javax.inject.Inject

interface SecurityHelper {
    fun verifyDevice(nonceInfo: String): Single<Result<String>>
}

class GoogleSecurityHelper @Inject constructor(
    @AppContext private val context: Context,
    @GoogleContext private val appKey: String
) : SecurityHelper {

    override fun verifyDevice(nonceInfo: String): Single<Result<String>> =
        Single.create<Result<String>> { emitter ->
            try {
                SafetyNet.getClient(context).attest(createNonce(nonceInfo), appKey)
                    .addOnCompleteListener { taskResult ->
                        if (emitter.isDisposed.not()) {
                            val jwsResult = taskResult.result?.jwsResult
                            val exception = taskResult.exception
                            val deviceValidationResult = when {
                                jwsResult != null -> Result.success(jwsResult)
                                exception != null -> Result.failure(exception)
                                else -> Result.failure(IllegalArgumentException())
                            }
                            emitter.onSuccess(deviceValidationResult)
                        }
                    }
            } catch (e: Exception) {
                if (emitter.isDisposed.not()) 
                    emitter.onSuccess(Result.failure(e))
            }
        }

    private fun createNonce(nonceInfo: String): ByteArray = ByteArrayOutputStream()
        .apply {
            
            write(/* some nonce bytes */)

        }.run {
            toByteArray()
        }

}