following working

src/BirdsiteLive.Domain/ActivityPubService.cs

@@ -1,17 +1,31 @@
-using System.Net.Http;
+using System;
+using System.Net;
+using System.Net.Http;
+using System.Text;
 using System.Threading.Tasks;
 using BirdsiteLive.ActivityPub;
 using Newtonsoft.Json;
+using Org.BouncyCastle.Bcpg;
 
 namespace BirdsiteLive.Domain
 {
     public interface IActivityPubService
     {
         Task<Actor> GetUser(string objectId);
+        Task<HttpStatusCode> PostDataAsync<T>(T data, string targetHost, string actorUrl);
     }
 
     public class ActivityPubService : IActivityPubService
     {
+        private readonly ICryptoService _cryptoService;
+
+        #region Ctor
+        public ActivityPubService(ICryptoService cryptoService)
+        {
+            _cryptoService = cryptoService;
+        }
+        #endregion
+
         public async Task<Actor> GetUser(string objectId)
         {
             using (var httpClient = new HttpClient())
@@ -22,5 +36,31 @@ namespace BirdsiteLive.Domain
                 return JsonConvert.DeserializeObject<Actor>(content);
             }
         }
+
+        public async Task<HttpStatusCode> PostDataAsync<T>(T data, string targetHost, string actorUrl)
+        {
+            var json = JsonConvert.SerializeObject(data);
+
+            var date = DateTime.UtcNow.ToUniversalTime();
+            var httpDate = date.ToString("r");
+            var signature = _cryptoService.SignAndGetSignatureHeader(date, actorUrl, targetHost);
+
+            var client = new HttpClient();
+            var httpRequestMessage = new HttpRequestMessage
+            {
+                Method = HttpMethod.Post,
+                RequestUri = new Uri($"https://{targetHost}/inbox"),
+                Headers =
+                {
+                    {"Host", targetHost},
+                    {"Date", httpDate},
+                    {"Signature", signature}
+                },
+                Content = new StringContent(json, Encoding.UTF8, "application/ld+json")
+            };
+
+            var response = await client.SendAsync(httpRequestMessage);
+            return response.StatusCode;
+        }
     }
 }

src/BirdsiteLive.Domain/UserService.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
+using System.Net;
 using System.Security.Cryptography;
 using System.Text;
 using System.Threading.Tasks;
@@ -71,9 +73,23 @@ namespace BirdsiteLive.Domain
             // Save Follow in DB
             
             // Send Accept Activity 
-
+            var targetHost = activity.actor.Replace("https://", string.Empty).Split('/').First();
-            
+            var acceptFollow = new ActivityAcceptFollow()
-            throw new NotImplementedException();
+            {
+                context = "https://www.w3.org/ns/activitystreams",
+                id = $"{activity.apObject}#accepts/follows/{Guid.NewGuid()}",
+                type = "Accept",
+                actor = activity.apObject,
+                apObject = new ActivityFollow()
+                {
+                    id = activity.id,
+                    type = activity.type,
+                    actor = activity.actor,
+                    apObject = activity.apObject
+                }
+            };
+            var result = await _activityPubService.PostDataAsync(acceptFollow, targetHost, activity.apObject);
+            return result == HttpStatusCode.Accepted;
         }
 
         private async Task<bool> ValidateSignature(string actor, string rawSig, string method, string path, string queryString, Dictionary<string, string> requestHeaders)

src/BirdsiteLive/Controllers/UsersController.cs

@@ -60,7 +60,7 @@ namespace BirdsiteLive.Controllers
                 {
                     case "Follow": 
                         var succeeded = await _userService.FollowRequestedAsync(r.Headers["Signature"].First(), r.Method, r.Path, r.QueryString.ToString(), RequestHeaders(r.Headers), activity as ActivityFollow);
-                        if (succeeded) return Ok();
+                        if (succeeded) return Accepted();
                         else return Unauthorized();
                         break;
                     default: