Get thread user implementation

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -525,7 +525,19 @@ namespace Discord.API
 
             var bucket = new BucketIds(channelId: channelId);
 
-            return await SendAsync<ThreadMember[]>("GET", () => $"channels/{channelId}/thread-members", bucket, options: options);
+            return await SendAsync<ThreadMember[]>("GET", () => $"channels/{channelId}/thread-members", bucket, options: options).ConfigureAwait(false);
+        }
+
+        public async Task<ThreadMember> GetThreadMemberAsync(ulong channelId, ulong userId, RequestOptions options = null)
+        {
+            Preconditions.NotEqual(channelId, 0, nameof(channelId));
+            Preconditions.NotEqual(userId, 0, nameof(userId));
+
+            options = RequestOptions.CreateOrClone(options);
+
+            var bucket = new BucketIds(channelId: channelId);
+
+            return await SendAsync<ThreadMember>("GET", () => $"channels/{channelId}/thread-members/{userId}", bucket, options: options).ConfigureAwait(false);
         }
 
         public async Task<ChannelThreads> GetActiveThreadsAsync(ulong channelId, RequestOptions options = null)

src/Discord.Net.Rest/Entities/Channels/ThreadHelper.cs

@@ -63,6 +63,10 @@ namespace Discord.Rest
         }
 
         public static async Task<RestThreadUser> GetUserAsync(ulong userId, IThreadChannel channel, BaseDiscordClient client, RequestOptions options = null)
-            => (await GetUsersAsync(channel, client, options).ConfigureAwait(false)).FirstOrDefault(x => x.Id == userId);
+        {
+            var model = await client.ApiClient.GetThreadMemberAsync(channel.Id, userId, options).ConfigureAwait(false);
+
+            return RestThreadUser.Create(client, channel.Guild, model, channel);
+        }
     }
 }