validation of the fediverse user

src/BirdsiteLive.Domain/ActivityPubService.cs

@@ -16,12 +16,19 @@ namespace BirdsiteLive.Domain
 {
     public interface IActivityPubService
     {
+        Task<string> GetUserIdAsync(string acct);
         Task<Actor> GetUser(string objectId);
         Task<HttpStatusCode> PostDataAsync<T>(T data, string targetHost, string actorUrl, string inbox = null);
         Task PostNewNoteActivity(Note note, string username, string noteId, string targetHost,
             string targetInbox);
     }
 
+    public class WebFinger
+    {
+        public string subject { get; set; }
+        public string[] aliases { get; set; }
+    }
+
     public class ActivityPubService : IActivityPubService
     {
         private readonly InstanceSettings _instanceSettings;
@@ -39,6 +46,24 @@ namespace BirdsiteLive.Domain
         }
         #endregion
 
+        public async Task<string> GetUserIdAsync(string acct)
+        {
+            var splittedAcct = acct.Trim('@').Split('@');
+
+            var url = $"https://{splittedAcct[1]}/.well-known/webfinger?resource=acct:{splittedAcct[0]}@{splittedAcct[1]}";
+
+            var httpClient = _httpClientFactory.CreateClient();
+            httpClient.DefaultRequestHeaders.Add("Accept", "application/json");
+            var result = await httpClient.GetAsync(url);
+
+            result.EnsureSuccessStatusCode();
+
+            var content = await result.Content.ReadAsStringAsync();
+
+            var actor = JsonConvert.DeserializeObject<WebFinger>(content);
+            return actor.aliases.FirstOrDefault();
+        }
+
         public async Task<Actor> GetUser(string objectId)
         {
             var httpClient = _httpClientFactory.CreateClient();

src/BirdsiteLive.Domain/MigrationService.cs

@@ -10,11 +10,13 @@ namespace BirdsiteLive.Domain
     public class MigrationService
     {
         private readonly ITwitterTweetsService _twitterTweetsService;
+        private readonly IActivityPubService _activityPubService;
 
         #region Ctor
-        public MigrationService(ITwitterTweetsService twitterTweetsService)
+        public MigrationService(ITwitterTweetsService twitterTweetsService, IActivityPubService activityPubService)
         {
             _twitterTweetsService = twitterTweetsService;
+            _activityPubService = activityPubService;
         }
         #endregion
 
@@ -52,11 +54,23 @@ namespace BirdsiteLive.Domain
 
         public async Task<bool> ValidateFediverseAcctAsync(string fediverseAcct)
         {
-            return true;
+            if (string.IsNullOrWhiteSpace(fediverseAcct))
+                throw new ArgumentException("Please provide Fediverse account");
+
+            if( !fediverseAcct.Contains('@') || fediverseAcct.Trim('@').Split('@').Length != 2)
+                throw new ArgumentException("Please provide valid Fediverse handle");
+
+            var objectId = await _activityPubService.GetUserIdAsync(fediverseAcct);
+            var user = await _activityPubService.GetUser(objectId);
+
+            if(user != null) return true;
+
+            return false;
         }
 
         public async Task MigrateAccountAsync(string acct, string tweetId, string fediverseAcct, bool triggerRemoteMigration)
         {
+            throw new NotImplementedException("Migration not implemented");
         }
 
         private byte[] GetHash(string inputString)