Changes needed on RetrofitHelper to add logics to refresh Auth0 token automatically

RetrofitHelper + Refresh Auth0 Token

object RetrofitHelper {

   (...)
   
   private fun rebuildRetrofit(useAuth: Boolean) {
        val client = buildOkHttpClient(useAuth)

        retrofit = Retrofit.Builder()
                .baseUrl(BuildConfig.API_BASE_URL)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create(buildGson()))
                .client(client)
                .build()
    }

    private fun buildOkHttpClient(useAuth: Boolean): OkHttpClient {
        this.usingAuth = useAuth
        var builder = OkHttpClient.Builder()
        builder = addLoggingInterceptor(builder)
        
        //This synchronized(builder) will make sure only one call to refresh the Auth0 token will be done at a time
        synchronized(builder) { builder = addTokenAuthenticator(builder) }
        
        return builder.build()
    }

    private fun addTokenAuthenticator(builder: OkHttpClient.Builder): OkHttpClient.Builder {

       //AUthenticator is called whenever a response is returned with 401 status code. In this case, you should refresh the token and perform the request again 
        val auth0Authenticator = object: Authenticator {
            override fun authenticate(route: Route?, response: Response): Request? {
                val accessToken = SessionHelper.instance.accessToken

                if (accessToken != null) {
                    val newAccessToken = SessionHelper.instance.refreshCredentials()
                    if (usingAuth && newAccessToken != null) {
                        return response.request().newBuilder().addHeader("Authorization", "Token $newAccessToken").addHeader("X-TOKEN-CLIENT-ID", clientId).build()
                    } else return null
                } else return null
            }
        }
        builder.authenticator(auth0Authenticator)

        // This interceptor will add the token to the header on every call, unless Authenticator has already added a new access token 
        val tokenInterceptor = Interceptor { chain ->
            var newRequest = chain.request()
            val accessToken = SessionHelper.instance.accessToken
            if (usingAuth && !accessToken.isNullOrBlank() && newRequest.header("Authorization").isNullOrBlank()) {
                newRequest = newRequest.newBuilder().addHeader("Authorization", "Token $accessToken").addHeader("X-TOKEN-CLIENT-ID", clientId).build()
            }
            chain.proceed(newRequest)
        }
        builder.addNetworkInterceptor(tokenInterceptor)

        return builder

    }

 }