Client side for calling an Azure function

AzureClient.cs

//Use this as a singleton in your app
public class AzureClient
{
    private const string BaseUrl = "https://YOUR_DOMAIN.azurewebsites.net/api/";
    private readonly HttpClient _client = new HttpClient();

    public async Task Verify(AppleReceipt receipt)
    {
        var content = new JsonContent(receipt);
        var response = await _client.PostAsync(BaseUrl + "ios?code=YOUR_CODE_HERE", content);
        response.EnsureSuccessStatusCode();
    }
}

//And the remaining bit in PurchaseService
public abstract class PurchaseService
{
    protected readonly AzureClient _client = new AzureClient();

    public async Task Buy(Purchase purchase)
    {
        var receipt = await BuyNative(purchase);

        var appleReceipt = receipt as AppleReceipt;
        if (appleReceipt != null)
        {
            await _client.Verify(appleReceipt);
            return;
        }

        //TODO: Google Play here
    }

    protected abstract Task<Receipt> BuyNative(Purchase purchase);
}