Add Duplicate Connection

src/Empostor.Api/Config/AntiCheatConfig.cs

@@ -38,6 +38,8 @@ namespace Empostor.Api.Config
 
         public bool EnableRateLimits { get; set; } = true;
 
+        public bool EnableDuplicateLoginCheck { get; set; } = true;
+
         public bool ForbidProtocolExtensions { get; set; } = true;
 
         public bool EnablePacketSizeChecks { get; set; } = true;

src/Empostor.Api/Games/GameJoinError.cs

@@ -54,5 +54,10 @@
         ///     A custom message can be set in <see cref="GameJoinResult.Message" />.
         /// </remarks>
         Custom,
+
+        /// <summary>
+        ///     The same account is already playing in this game.
+        /// </summary>
+        DuplicateConnection,
     }
 }

src/Empostor.Server/Net/Client.cs

@@ -221,6 +221,9 @@ namespace Empostor.Server.Net
                         case GameJoinError.Custom:
                             await DisconnectAsync(DisconnectReason.Custom, result.Message);
                             break;
+                        case GameJoinError.DuplicateConnection:
+                            await DisconnectAsync(DisconnectReason.DuplicateConnectionDetected);
+                            break;
                         default:
                             await DisconnectAsync(DisconnectReason.Custom, "Unknown error.");
                             break;

src/Empostor.Server/Net/State/Game.Incoming.cs

@@ -2,6 +2,7 @@ using System;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Empostor.Api.Config;
 using Empostor.Api.Games;
 using Empostor.Api.Net;
 using Next.Hazel;
@@ -118,8 +119,7 @@ namespace Empostor.Server.Net.State
             return GameJoinResult.FromError(GameJoinError.InvalidClient);
         }
 
-        private async ValueTask HandleJoinGameNew(ClientPlayer sender, bool isNew)
-        {
+        private async ValueTask HandleJoinGameNew(ClientPlayer sender, bool isNew)        {
             var client = sender.Client;
             var authority = client.GameVersion.HasDisableServerAuthorityFlag ? "true" : "false";
             var version = client.GameVersion.ToString();
@@ -155,6 +155,29 @@ namespace Empostor.Server.Net.State
             }
         }
 
+        private bool IsDuplicateAccount(ClientBase client)
+        {
+            if (string.IsNullOrEmpty(client.ProductUserId))
+            {
+                return false;
+            }
+
+            foreach (var other in _players.Values)
+            {
+                if (other.Client == client)
+                {
+                    continue;
+                }
+
+                if (string.Equals(other.Client.ProductUserId, client.ProductUserId, StringComparison.OrdinalIgnoreCase))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
         private async ValueTask<GameJoinResult> AddClientSafeAsync(ClientBase client)
         {
             if (_bannedIps.Contains(client.Connection.EndPoint.Address))
@@ -163,6 +186,15 @@ namespace Empostor.Server.Net.State
             }
 
             var player = client.Player;
+            if (AntiCheat.Config.EnableDuplicateLoginCheck && IsDuplicateAccount(client))
+            {
+                _logger.LogWarning(
+                    "#{Id} {Name} rejected: account {Puid} is already playing in this game",
+                    client.Id, client.Name, client.ProductUserId);
+
+                return GameJoinResult.FromError(GameJoinError.DuplicateConnection);
+            }
+
             if (_compatibilityConfig.AllowVersionMixing == false &&
                 this.Host != null && client.GameVersion != this.Host.Client.GameVersion)
             {

src/Empostor.Server/config.json

@@ -32,6 +32,7 @@
     "EnableMeetingChecks": true,
     "EnableVotingChecks": true,
     "EnableRateLimits": true,
+    "EnableDuplicateLoginCheck": true,
     "ForbidProtocolExtensions": true,
     "EnablePacketSizeChecks": true,
     "PacketSizeLimit": 1203