paypal client and stub out webhook

src/Billing/Controllers/PaypalController.cs

@@ -0,0 +1,56 @@
+using Bit.Billing.Utilities;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Options;
+using Newtonsoft.Json;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Bit.Billing.Controllers
+{
+    [Route("paypal")]
+    public class PaypalController : Controller
+    {
+        private readonly BillingSettings _billingSettings;
+        private readonly PaypalClient _paypalClient;
+
+        public PaypalController(
+            IOptions<BillingSettings> billingSettings,
+            PaypalClient paypalClient)
+        {
+            _billingSettings = billingSettings?.Value;
+            _paypalClient = paypalClient;
+        }
+
+        [HttpPost("webhook")]
+        public async Task<IActionResult> PostWebhook([FromQuery] string key)
+        {
+            if(HttpContext?.Request == null)
+            {
+                return new BadRequestResult();
+            }
+
+            string body = null;
+            using(var reader = new StreamReader(HttpContext.Request.Body, Encoding.UTF8))
+            {
+                body = await reader.ReadToEndAsync();
+            }
+
+            if(body == null)
+            {
+                return new BadRequestResult();
+            }
+
+            var verified = await _paypalClient.VerifyWebhookAsync(body, HttpContext.Request.Headers,
+                _billingSettings.Paypal.WebhookId);
+            if(!verified)
+            {
+                return new BadRequestResult();
+            }
+
+            var webhook = JsonConvert.DeserializeObject(body);
+            // TODO: process webhook
+            return new OkResult();
+        }
+    }
+}