From 2535751cd9f61cbc880032decb3c20c3dac32f7e Mon Sep 17 00:00:00 2001
From: Rocco <hey@rocco.dev>
Date: Tue, 10 Feb 2026 18:59:34 +0000
Subject: [PATCH] Add server-id hash to LoginEvent (#1027)

---
 .../api/event/connection/LoginEvent.java      | 28 ++++++++++++++++++-
 .../connection/client/AuthSessionHandler.java |  6 ++--
 .../client/InitialLoginSessionHandler.java    |  4 +--
 3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/api/src/main/java/com/velocitypowered/api/event/connection/LoginEvent.java b/api/src/main/java/com/velocitypowered/api/event/connection/LoginEvent.java
index 3ec012649..29997670f 100644
--- a/api/src/main/java/com/velocitypowered/api/event/connection/LoginEvent.java
+++ b/api/src/main/java/com/velocitypowered/api/event/connection/LoginEvent.java
@@ -11,6 +11,7 @@ import com.google.common.base.Preconditions;
 import com.velocitypowered.api.event.ResultedEvent;
 import com.velocitypowered.api.event.annotation.AwaitingEvent;
 import com.velocitypowered.api.proxy.Player;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * This event is fired once the player has been authenticated, but before they connect to a server.
@@ -22,18 +23,33 @@ import com.velocitypowered.api.proxy.Player;
 public final class LoginEvent implements ResultedEvent<ResultedEvent.ComponentResult> {
 
   private final Player player;
+  private final String serverIdHash;
   private ComponentResult result;
 
   /**
    * Constructs a new {@link LoginEvent}.
    *
    * @param player the player who has completed authentication
+   * @param serverIdHash the server ID hash sent to Mojang for authentication,
+   *                     or {@code null} if the connection is in offline-mode
    */
-  public LoginEvent(Player player) {
+  public LoginEvent(Player player, @Nullable String serverIdHash) {
     this.player = Preconditions.checkNotNull(player, "player");
+    this.serverIdHash = serverIdHash;
     this.result = ComponentResult.allowed();
   }
 
+  /**
+   * Constructs a new {@link LoginEvent}.
+   *
+   * @param player the player who has completed authentication
+   * @deprecated Use {@link #LoginEvent(Player, String)}.
+   */
+  @Deprecated(forRemoval = true)
+  public LoginEvent(Player player) {
+    this(player, null);
+  }
+
   /**
    * Returns the player who has completed authentication.
    *
@@ -43,6 +59,16 @@ public final class LoginEvent implements ResultedEvent<ResultedEvent.ComponentRe
     return player;
   }
 
+  /**
+   * Returns the server ID hash that was sent to Mojang to authenticate the player.
+   * If the connection was in offline-mode, this returns {@code null}.
+   *
+   * @return the server ID hash that was sent to Mojang to authenticate the player
+   */
+  public @Nullable String getServerIdHash() {
+    return serverIdHash;
+  }
+
   @Override
   public ComponentResult getResult() {
     return result;
diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/AuthSessionHandler.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/AuthSessionHandler.java
index 0aea8d778..605388ea3 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/AuthSessionHandler.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/AuthSessionHandler.java
@@ -69,14 +69,16 @@ public class AuthSessionHandler implements MinecraftSessionHandler {
   private @MonotonicNonNull ConnectedPlayer connectedPlayer;
   private final boolean onlineMode;
   private State loginState = State.START; // 1.20.2+
+  private final String serverIdHash;
 
   AuthSessionHandler(VelocityServer server, LoginInboundConnection inbound,
-      GameProfile profile, boolean onlineMode) {
+      GameProfile profile, boolean onlineMode, String serverIdHash) {
     this.server = Preconditions.checkNotNull(server, "server");
     this.inbound = Preconditions.checkNotNull(inbound, "inbound");
     this.profile = Preconditions.checkNotNull(profile, "profile");
     this.onlineMode = onlineMode;
     this.mcConnection = inbound.delegatedConnection();
+    this.serverIdHash = serverIdHash;
   }
 
   @Override
@@ -213,7 +215,7 @@ public class AuthSessionHandler implements MinecraftSessionHandler {
   private void completeLoginProtocolPhaseAndInitialize(ConnectedPlayer player) {
     mcConnection.setAssociation(player);
 
-    server.getEventManager().fire(new LoginEvent(player)).thenAcceptAsync(event -> {
+    server.getEventManager().fire(new LoginEvent(player, serverIdHash)).thenAcceptAsync(event -> {
       if (mcConnection.isClosed()) {
         // The player was disconnected
         server.getEventManager().fireAndForget(new DisconnectEvent(player,
diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/InitialLoginSessionHandler.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/InitialLoginSessionHandler.java
index 92f14191c..482fb76e6 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/InitialLoginSessionHandler.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/InitialLoginSessionHandler.java
@@ -152,7 +152,7 @@ public class InitialLoginSessionHandler implements MinecraftSessionHandler {
           } else {
             mcConnection.setActiveSessionHandler(StateRegistry.LOGIN,
                 new AuthSessionHandler(server, inbound,
-                    GameProfile.forOfflinePlayer(login.getUsername()), false));
+                    GameProfile.forOfflinePlayer(login.getUsername()), false, null));
           }
         });
       });
@@ -255,7 +255,7 @@ public class InitialLoginSessionHandler implements MinecraftSessionHandler {
               }
               // All went well, initialize the session.
               mcConnection.setActiveSessionHandler(StateRegistry.LOGIN,
-                  new AuthSessionHandler(server, inbound, profile, true));
+                  new AuthSessionHandler(server, inbound, profile, true, serverId));
             } else if (response.statusCode() == 204) {
               // Apparently an offline-mode user logged onto this online-mode proxy.
               inbound.disconnect(