diff --git a/Minecraft.Client/AuthScreen.cpp b/Minecraft.Client/AuthScreen.cpp
index 0f0d3330..bdaa2b9b 100644
--- a/Minecraft.Client/AuthScreen.cpp
+++ b/Minecraft.Client/AuthScreen.cpp
@@ -3,6 +3,7 @@
 #include "Minecraft.h"
 #include "User.h"
 #include "..\Minecraft.World\AuthModule.h"
+#include "..\Minecraft.World\SessionAuthModule.h"
 #include "..\Minecraft.World\HttpClient.h"
 #include "..\Minecraft.World\StringHelpers.h"
 #include "Common/vendor/nlohmann/json.hpp"
@@ -12,24 +13,33 @@
 
 using json = nlohmann::json;
 static constexpr auto PROFILES_FILE = L"auth_profiles.dat";
-static constexpr auto MS_CLIENT_ID = "00000000441cc96b";
+static constexpr auto MS_CLIENT_ID = "00000000402b5328";
 static json parseResponse(const HttpResponse &resp, int expectedStatus = 200);
 static bool msTokenExchange(const string &msAccessToken, string &mcToken, string &profId, string &profName);
 static bool msRefreshOAuth(const string &refreshToken, string &newAccessToken, string &newRefreshToken);
-static bool elybyValidate(const string &accessToken, const string &clientToken);
-static bool elybyRefresh(const string &accessToken, const string &clientToken, string &newAccessToken, string &newClientToken);
+static bool yggdrasilValidate(const string &accessToken, const string &clientToken, const string &validateUrl);
+static bool yggdrasilRefresh(const string &accessToken, const string &clientToken, string &newAccessToken, string &newClientToken, const string &refreshUrl);
 
 vector<AuthProfile> AuthProfileManager::profiles;
 int AuthProfileManager::selectedProfile = -1;
 
+static constexpr uint32_t PROFILE_MAGIC = 0x4D435032;
+
 void AuthProfileManager::load()
 {
 	profiles.clear();
 	std::ifstream file(PROFILES_FILE, std::ios::binary);
 	if (!file) return;
 
+	uint32_t header = 0;
+	file.read(reinterpret_cast<char *>(&header), sizeof(header));
+	bool hasVariation = (header == PROFILE_MAGIC);
+
 	uint32_t count = 0;
-	file.read(reinterpret_cast<char *>(&count), sizeof(count));
+	if (hasVariation)
+		file.read(reinterpret_cast<char *>(&count), sizeof(count));
+	else
+		count = header;
 
 	for (uint32_t i = 0; i < count && file.good(); i++)
 	{
@@ -52,6 +62,10 @@ void AuthProfileManager::load()
 		p.username = readWstr();
 		p.token = readWstr();
 		p.clientToken = readWstr();
+		if (hasVariation)
+			p.variation = readWstr();
+		if (p.variation.empty() && p.type == AuthProfile::YGGDRASIL)
+			p.variation = L"elyby";
 		profiles.push_back(std::move(p));
 	}
 
@@ -66,6 +80,9 @@ void AuthProfileManager::save()
 	std::ofstream file(PROFILES_FILE, std::ios::binary | std::ios::trunc);
 	if (!file) return;
 
+	uint32_t magic = PROFILE_MAGIC;
+	file.write(reinterpret_cast<const char *>(&magic), sizeof(magic));
+
 	uint32_t count = static_cast<uint32_t>(profiles.size());
 	file.write(reinterpret_cast<const char *>(&count), sizeof(count));
 
@@ -83,16 +100,17 @@ void AuthProfileManager::save()
 		writeWstr(p.username);
 		writeWstr(p.token);
 		writeWstr(p.clientToken);
+		writeWstr(p.variation);
 	}
 
 	int32_t idx = static_cast<int32_t>(selectedProfile);
 	file.write(reinterpret_cast<const char *>(&idx), sizeof(idx));
 }
 
-void AuthProfileManager::addProfile(AuthProfile::Type type, const wstring &username, const wstring &uid, const wstring &token, const wstring &clientToken)
+void AuthProfileManager::addProfile(AuthProfile::Type type, const wstring &username, const wstring &uid, const wstring &token, const wstring &clientToken, const wstring &variation)
 {
 	wstring finalUid = uid.empty() ? L"offline_" + username : uid;
-	profiles.push_back({type, finalUid, username, token, clientToken});
+	profiles.push_back({type, finalUid, username, token, clientToken, variation});
 	selectedProfile = static_cast<int>(profiles.size()) - 1;
 	save();
 }
@@ -137,12 +155,14 @@ bool AuthProfileManager::applySelectedProfile()
 			}
 		}
 	}
-	else if (p.type == AuthProfile::ELYBY && !p.token.empty())
+	else if (p.type == AuthProfile::YGGDRASIL && !p.token.empty())
 	{
-		if (!elybyValidate(narrowStr(p.token), narrowStr(p.clientToken)))
+		auto *provider = YggdrasilRegistry::find(p.variation);
+		if (!provider) provider = &YggdrasilRegistry::defaultProvider();
+		if (!yggdrasilValidate(narrowStr(p.token), narrowStr(p.clientToken), provider->validateUrl()))
 		{
 			string newAccess, newClient;
-			if (elybyRefresh(narrowStr(p.token), narrowStr(p.clientToken), newAccess, newClient))
+			if (yggdrasilRefresh(narrowStr(p.token), narrowStr(p.clientToken), newAccess, newClient, provider->refreshUrl()))
 			{
 				p.token = convStringToWstring(newAccess);
 				if (!newClient.empty()) p.clientToken = convStringToWstring(newClient);
@@ -169,7 +189,6 @@ bool AuthProfileManager::applySelectedProfile()
 	return true;
 }
 
-// --- AuthFlow ---
 
 std::thread AuthFlow::workerThread;
 std::atomic<AuthFlowState> AuthFlow::state{AuthFlowState::IDLE};
@@ -177,6 +196,7 @@ std::atomic<bool> AuthFlow::cancelRequested{false};
 AuthResult AuthFlow::result;
 wstring AuthFlow::userCode;
 wstring AuthFlow::verificationUri;
+wstring AuthFlow::activeVariation;
 
 void AuthFlow::reset()
 {
@@ -187,6 +207,7 @@ void AuthFlow::reset()
 	result = {};
 	userCode.clear();
 	verificationUri.clear();
+	activeVariation.clear();
 	cancelRequested = false;
 }
 
@@ -197,11 +218,15 @@ void AuthFlow::startMicrosoft()
 	workerThread = std::thread(microsoftFlowThread);
 }
 
-void AuthFlow::startElyBy(const wstring &username, const wstring &password)
+void AuthFlow::startYggdrasil(const wstring &username, const wstring &password, const wstring &providerName)
 {
 	reset();
 	state = AuthFlowState::EXCHANGING;
-	workerThread = std::thread(elybyFlowThread, narrowStr(username), narrowStr(password));
+	wstring resolvedName = providerName.empty() ? YggdrasilRegistry::defaultProvider().name : providerName;
+	activeVariation = resolvedName;
+	auto *provider = YggdrasilRegistry::find(resolvedName);
+	string authUrl = provider ? provider->authenticateUrl() : YggdrasilRegistry::defaultProvider().authenticateUrl();
+	workerThread = std::thread(yggdrasilFlowThread, narrowStr(username), narrowStr(password), authUrl);
 }
 
 static void authFail(AuthResult &result, std::atomic<AuthFlowState> &state, const wchar_t *msg)
@@ -210,7 +235,6 @@ static void authFail(AuthResult &result, std::atomic<AuthFlowState> &state, cons
 	state = AuthFlowState::FAILED;
 }
 
-// parse json response body, return discarded json on bad status
 static json parseResponse(const HttpResponse &resp, int expectedStatus)
 {
 	if (resp.statusCode != expectedStatus) return json::value_t::discarded;
@@ -273,19 +297,15 @@ static bool msRefreshOAuth(const string &refreshToken, string &newAccessToken, s
 	newRefreshToken = j.value("refresh_token", "");
 	return !newAccessToken.empty();
 }
-
-// validate ely.by token via yggdrasil /validate endpoint
-static bool elybyValidate(const string &accessToken, const string &clientToken)
+static bool yggdrasilValidate(const string &accessToken, const string &clientToken, const string &validateUrl)
 {
-	auto resp = HttpClient::post("https://authserver.ely.by/auth/validate",
+	auto resp = HttpClient::post(validateUrl,
 		json({{"accessToken", accessToken}, {"clientToken", clientToken}}).dump());
 	return resp.statusCode == 200;
 }
-
-// refresh ely.by token via yggdrasil /refresh endpoint
-static bool elybyRefresh(const string &accessToken, const string &clientToken, string &newAccessToken, string &newClientToken)
+static bool yggdrasilRefresh(const string &accessToken, const string &clientToken, string &newAccessToken, string &newClientToken, const string &refreshUrl)
 {
-	auto resp = HttpClient::post("https://authserver.ely.by/auth/refresh",
+	auto resp = HttpClient::post(refreshUrl,
 		json({{"accessToken", accessToken}, {"clientToken", clientToken}}).dump());
 
 	auto j = parseResponse(resp);
@@ -403,9 +423,9 @@ void AuthFlow::microsoftFlowThread()
 	state = AuthFlowState::COMPLETE;
 }
 
-void AuthFlow::elybyFlowThread(const string &username, const string &password)
+void AuthFlow::yggdrasilFlowThread(const string &username, const string &password, const string &authenticateUrl)
 {
-	auto resp = HttpClient::post("https://authserver.ely.by/auth/authenticate", json({
+	auto resp = HttpClient::post(authenticateUrl, json({
 		{"username", username},
 		{"password", password},
 		{"clientToken", "mcconsoles"},
@@ -416,7 +436,7 @@ void AuthFlow::elybyFlowThread(const string &username, const string &password)
 
 	if (resp.statusCode != 200 || respJson.is_discarded())
 	{
-		string msg = "Ely.by auth failed";
+		string msg = "Yggdrasil auth failed";
 		if (!respJson.is_discarded()) msg = respJson.value("errorMessage", msg);
 		result = {false, {}, {}, {}, {}, convStringToWstring(msg)};
 		state = AuthFlowState::FAILED;
@@ -424,16 +444,16 @@ void AuthFlow::elybyFlowThread(const string &username, const string &password)
 	}
 
 	string accessToken = respJson.value("accessToken", "");
-	string elyClientToken = respJson.value("clientToken", "");
+	string yggClientToken = respJson.value("clientToken", "");
 	string uuid, name;
 	try { uuid = respJson["selectedProfile"].value("id", ""); name = respJson["selectedProfile"].value("name", ""); } catch (...) {}
 
 	if (accessToken.empty() || uuid.empty() || name.empty())
 	{
-		authFail(result, state, L"Ely.by response missing profile");
+		authFail(result, state, L"Yggdrasil response missing profile");
 		return;
 	}
 
-	result = {true, convStringToWstring(name), convStringToWstring(uuid), convStringToWstring(accessToken), convStringToWstring(elyClientToken), {}};
+	result = {true, convStringToWstring(name), convStringToWstring(uuid), convStringToWstring(accessToken), convStringToWstring(yggClientToken), {}};
 	state = AuthFlowState::COMPLETE;
 }
diff --git a/Minecraft.Client/AuthScreen.h b/Minecraft.Client/AuthScreen.h
index c24afc26..38425f0c 100644
--- a/Minecraft.Client/AuthScreen.h
+++ b/Minecraft.Client/AuthScreen.h
@@ -5,13 +5,14 @@ using namespace std;
 
 struct AuthProfile
 {
-	enum Type : uint8_t { MICROSOFT, ELYBY, OFFLINE };
+	enum Type : uint8_t { MICROSOFT, YGGDRASIL, OFFLINE };
 
 	Type type;
 	wstring uid;
 	wstring username;
 	wstring token;
 	wstring clientToken;
+	wstring variation;
 };
 
 class AuthProfileManager
@@ -23,7 +24,7 @@ private:
 public:
 	static void load();
 	static void save();
-	static void addProfile(AuthProfile::Type type, const wstring &username, const wstring &uid = L"", const wstring &token = L"", const wstring &clientToken = L"");
+	static void addProfile(AuthProfile::Type type, const wstring &username, const wstring &uid = L"", const wstring &token = L"", const wstring &clientToken = L"", const wstring &variation = L"");
 	static void removeSelectedProfile();
 	static bool applySelectedProfile();
 
@@ -60,17 +61,17 @@ private:
 	static AuthResult result;
 	static wstring userCode;
 	static wstring verificationUri;
-
+	static wstring activeVariation;
 	static void microsoftFlowThread();
-	static void elybyFlowThread(const string &username, const string &password);
+	static void yggdrasilFlowThread(const string &username, const string &password, const string &authenticateUrl);
 
 public:
 	static void startMicrosoft();
-	static void startElyBy(const wstring &username, const wstring &password);
-
+	static void startYggdrasil(const wstring &username, const wstring &password, const wstring &providerName = L"");
 	static AuthFlowState getState() { return state.load(); }
 	static const AuthResult &getResult() { return result; }
 	static const wstring &getUserCode() { return userCode; }
 	static const wstring &getVerificationUri() { return verificationUri; }
+	static const wstring &getActiveVariation() { return activeVariation; }
 	static void reset();
 };
diff --git a/Minecraft.Client/CMakeLists.txt b/Minecraft.Client/CMakeLists.txt
index 9f75efd2..9f52cd53 100644
--- a/Minecraft.Client/CMakeLists.txt
+++ b/Minecraft.Client/CMakeLists.txt
@@ -44,6 +44,8 @@ set_source_files_properties(compat_shims.cpp PROPERTIES SKIP_PRECOMPILE_HEADERS
 
 configure_compiler_target(Minecraft.Client)
 
+target_link_options(Minecraft.Client PRIVATE "/MAP")
+
 set_target_properties(Minecraft.Client PROPERTIES
   OUTPUT_NAME "Minecraft.Client"
   VS_DEBUGGER_WORKING_DIRECTORY "$<TARGET_FILE_DIR:Minecraft.Client>"
diff --git a/Minecraft.Client/ClientConnection.cpp b/Minecraft.Client/ClientConnection.cpp
index 2765e921..23585e8e 100644
--- a/Minecraft.Client/ClientConnection.cpp
+++ b/Minecraft.Client/ClientConnection.cpp
@@ -56,7 +56,6 @@
 #include "DLCTexturePack.h"
 #include "..\Minecraft.World\HandshakeManager.h"
 #include "..\Minecraft.World\SessionAuthModule.h"
-#include "..\Minecraft.World\OfflineAuthModule.h"
 #include "AuthScreen.h"
 
 #ifdef _WINDOWS64
@@ -4141,21 +4140,33 @@ ClientConnection::DeferredEntityLinkPacket::DeferredEntityLinkPacket(shared_ptr<
 
 void ClientConnection::beginAuth()
 {
+	app.DebugPrintf("AUTH: beginAuth() starting\n");
 	handshakeManager = new HandshakeManager(false);
-	handshakeManager->registerModule(std::make_unique<SessionAuthModule>());
-	handshakeManager->registerModule(std::make_unique<KeypairOfflineAuthModule>());
-	handshakeManager->registerModule(std::make_unique<OfflineAuthModule>());
 
 	const auto &profiles = AuthProfileManager::getProfiles();
 	int idx = AuthProfileManager::getSelectedIndex();
+	bool isOffline = true;
 	if (idx >= 0 && idx < static_cast<int>(profiles.size()))
 	{
 		const auto &p = profiles[idx];
+		isOffline = (p.type == AuthProfile::OFFLINE);
 		wstring variation;
 		if (p.type == AuthProfile::MICROSOFT) variation = L"mojang";
-		else if (p.type == AuthProfile::ELYBY) variation = L"elyby";
+		else if (p.type == AuthProfile::YGGDRASIL) variation = p.variation;
+		app.DebugPrintf("AUTH: profile type=%d variation=%ls username=%ls\n",
+			(int)p.type, variation.c_str(), p.username.c_str());
 		handshakeManager->setCredentials(p.token, p.uid, p.username, variation);
 	}
+	else
+	{
+		app.DebugPrintf("AUTH: no valid profile selected (idx=%d, count=%d)\n",
+			idx, (int)profiles.size());
+	}
+
+	if (!isOffline)
+		handshakeManager->registerModule(std::make_unique<SessionAuthModule>());
+	handshakeManager->registerModule(std::make_unique<KeypairOfflineAuthModule>());
+	handshakeManager->registerModule(std::make_unique<OfflineAuthModule>());
 
 	auto initial = handshakeManager->createInitialPacket();
 	if (initial) send(initial);
diff --git a/Minecraft.Client/Common/Network/GameNetworkManager.cpp b/Minecraft.Client/Common/Network/GameNetworkManager.cpp
index 50aeae68..934a9105 100644
--- a/Minecraft.Client/Common/Network/GameNetworkManager.cpp
+++ b/Minecraft.Client/Common/Network/GameNetworkManager.cpp
@@ -413,6 +413,35 @@ bool	CGameNetworkManager::StartNetworkGame(Minecraft *minecraft, LPVOID lpParame
 			return false;
 		}
 
+		if (!g_NetworkManager.IsHost())
+		{
+			try {
+			connection->beginAuth();
+			while (!connection->authComplete && !connection->isClosed() && IsInSession() && !g_NetworkManager.IsLeavingGame())
+			{
+				connection->tick();
+				Sleep(50);
+			}
+			} catch (...) {
+				app.DebugPrintf("AUTH: exception during auth handshake\n");
+				connection->close();
+				delete connection;
+				connection = nullptr;
+				MinecraftServer::HaltServer();
+				return false;
+			}
+
+			if (!connection->authComplete)
+			{
+				app.DebugPrintf("Auth handshake did not complete, aborting connection\n");
+				connection->close();
+				delete connection;
+				connection = nullptr;
+				MinecraftServer::HaltServer();
+				return false;
+			}
+		}
+
 		connection->send(std::make_shared<PreLoginPacket>(minecraft->user->name));
 
 	// Tick connection until we're ready to go. The stages involved in this are:
diff --git a/Minecraft.Client/Common/UI/UIScene_MainMenu.cpp b/Minecraft.Client/Common/UI/UIScene_MainMenu.cpp
index 3d1febc3..4070de8b 100644
--- a/Minecraft.Client/Common/UI/UIScene_MainMenu.cpp
+++ b/Minecraft.Client/Common/UI/UIScene_MainMenu.cpp
@@ -2,6 +2,7 @@
 #include "..\..\..\Minecraft.World\Mth.h"
 #include "..\..\..\Minecraft.World\StringHelpers.h"
 #include "..\..\..\Minecraft.World\Random.h"
+#include "..\..\..\Minecraft.World\SessionAuthModule.h"
 #include "..\..\User.h"
 #include "..\..\MinecraftServer.h"
 #include "..\..\AuthScreen.h"
@@ -459,7 +460,7 @@ void UIScene_MainMenu::RunAction(int iPad)
 
 static int s_authPad = 0;
 static void *s_authParam = nullptr;
-static wstring s_elybyUsername;
+static wstring s_yggdrasilUsername;
 static bool s_authFlowActive = false;
 
 static wstring ReadKeyboardText(int maxLen)
@@ -509,11 +510,17 @@ static const wchar_t *BuildAuthProfileText()
 		for (int i = 0; i < static_cast<int>(profiles.size()); i++)
 		{
 			const auto &p = profiles[i];
-			const wchar_t *type = (p.type == AuthProfile::MICROSOFT) ? L"[MS]"
-				: (p.type == AuthProfile::ELYBY) ? L"[Ely]" : L"[Off]";
+			wstring label;
+			if (p.type == AuthProfile::MICROSOFT) label = L"[MS]";
+			else if (p.type == AuthProfile::YGGDRASIL)
+			{
+				auto *provider = YggdrasilRegistry::find(p.variation);
+				label = provider ? L"[" + provider->displayName + L"]" : L"[Ygg]";
+			}
+			else label = L"[Off]";
 			if (i > 0) text += L"\n";
 			text += (i == sel) ? L"> " : L"  ";
-			text += wstring(type) + L" " + p.username;
+			text += label + L" " + p.username;
 		}
 	}
 	return text.c_str();
@@ -531,7 +538,9 @@ void UIScene_MainMenu::ShowAuthMenu(int iPad, void *pClass)
 
 void UIScene_MainMenu::ShowAuthAddMenu(int iPad, void *pClass)
 {
-	static const wchar_t *addOptions[] = { L"Microsoft Auth", L"Ely.by Auth", L"Add Offline User", L"Back" };
+	static wstring yggLabel;
+	yggLabel = YggdrasilRegistry::defaultProvider().displayName + L" Auth";
+	const wchar_t *addOptions[] = { L"Microsoft Auth", yggLabel.c_str(), L"Add Offline User", L"Back" };
 	ShowAuthMessageBox(iPad, L"Add Profile", L"Select an auth type",
 		addOptions, 4, &UIScene_MainMenu::AuthAddMenuReturned, pClass);
 }
@@ -602,15 +611,15 @@ int UIScene_MainMenu::AuthAddMenuReturned(LPVOID lpParam, int iPad, const C4JSto
 	{
 #ifdef _WINDOWS64
 		UIKeyboardInitData kbData;
-		kbData.title = L"Ely.by Username";
+		kbData.title = L"Username";
 		kbData.defaultText = L"";
 		kbData.maxChars = 64;
-		kbData.callback = &UIScene_MainMenu::ElyByUsernameReturned;
+		kbData.callback = &UIScene_MainMenu::YggdrasilUsernameReturned;
 		kbData.lpParam = lpParam;
 		kbData.pcMode = g_KBMInput.IsKBMActive();
 		ui.NavigateToScene(iPad, eUIScene_Keyboard, &kbData);
 #else
-		InputManager.RequestKeyboard(L"Ely.by Username", L"", (DWORD)0, 64, &UIScene_MainMenu::ElyByUsernameReturned, lpParam, C_4JInput::EKeyboardMode_Default);
+		InputManager.RequestKeyboard(L"Username", L"", (DWORD)0, 64, &UIScene_MainMenu::YggdrasilUsernameReturned, lpParam, C_4JInput::EKeyboardMode_Default);
 #endif
 		break;
 	}
@@ -646,26 +655,26 @@ int UIScene_MainMenu::AuthMsFlowReturned(LPVOID lpParam, int iPad, const C4JStor
 	return 0;
 }
 
-int UIScene_MainMenu::ElyByUsernameReturned(LPVOID lpParam, const bool bRes)
+int UIScene_MainMenu::YggdrasilUsernameReturned(LPVOID lpParam, const bool bRes)
 {
 	if (bRes)
 	{
 		wstring name = ReadKeyboardText(128);
 		if (!name.empty())
 		{
-			s_elybyUsername = std::move(name);
+			s_yggdrasilUsername = std::move(name);
 #ifdef _WINDOWS64
 			UIKeyboardInitData kbData;
-			kbData.title = L"Ely.by Password";
+			kbData.title = L"Password";
 			kbData.defaultText = L"";
 			kbData.maxChars = 128;
-			kbData.callback = &UIScene_MainMenu::ElyByPasswordReturned;
+			kbData.callback = &UIScene_MainMenu::YggdrasilPasswordReturned;
 			kbData.lpParam = lpParam;
 			kbData.pcMode = g_KBMInput.IsKBMActive();
 			kbData.keyboardMode = C_4JInput::EKeyboardMode_Password;
 			ui.NavigateToScene(s_authPad, eUIScene_Keyboard, &kbData);
 #else
-			InputManager.RequestKeyboard(L"Ely.by Password", L"", (DWORD)0, 128, &UIScene_MainMenu::ElyByPasswordReturned, lpParam, C_4JInput::EKeyboardMode_Password);
+			InputManager.RequestKeyboard(L"Password", L"", (DWORD)0, 128, &UIScene_MainMenu::YggdrasilPasswordReturned, lpParam, C_4JInput::EKeyboardMode_Password);
 #endif
 			return 0;
 		}
@@ -674,18 +683,20 @@ int UIScene_MainMenu::ElyByUsernameReturned(LPVOID lpParam, const bool bRes)
 	return 0;
 }
 
-int UIScene_MainMenu::ElyByPasswordReturned(LPVOID lpParam, const bool bRes)
+int UIScene_MainMenu::YggdrasilPasswordReturned(LPVOID lpParam, const bool bRes)
 {
 	if (bRes)
 	{
 		wstring pass = ReadKeyboardText(256);
 		if (!pass.empty())
 		{
-			AuthFlow::startElyBy(s_elybyUsername, pass);
+			AuthFlow::startYggdrasil(s_yggdrasilUsername, pass);
 			s_authFlowActive = true;
 
+			static wstring loginTitle;
+			loginTitle = YggdrasilRegistry::defaultProvider().displayName + L" Login";
 			static const wchar_t *waitOptions[] = { L"Cancel" };
-			ShowAuthMessageBox(s_authPad, L"Ely.by Login", L"Authenticating...",
+			ShowAuthMessageBox(s_authPad, loginTitle.c_str(), L"Authenticating...",
 				waitOptions, 1, &UIScene_MainMenu::AuthMsFlowReturned, lpParam, true);
 
 			SecureZeroMemory(pass.data(), pass.size() * sizeof(wchar_t));
@@ -2144,8 +2155,9 @@ void UIScene_MainMenu::tick()
 		{
 			s_authFlowActive = false;
 			const auto &r = AuthFlow::getResult();
-			auto type = AuthFlow::getUserCode().empty() ? AuthProfile::ELYBY : AuthProfile::MICROSOFT;
-			AuthProfileManager::addProfile(type, r.username, r.uuid, r.accessToken, r.clientToken);
+			auto type = AuthFlow::getUserCode().empty() ? AuthProfile::YGGDRASIL : AuthProfile::MICROSOFT;
+			wstring variation = (type == AuthProfile::YGGDRASIL) ? AuthFlow::getActiveVariation() : L"";
+			AuthProfileManager::addProfile(type, r.username, r.uuid, r.accessToken, r.clientToken, variation);
 			AuthFlow::reset();
 			if (scene) ui.NavigateBack(s_authPad);
 			ShowAuthMenu(s_authPad, s_authParam);
diff --git a/Minecraft.Client/Common/UI/UIScene_MainMenu.h b/Minecraft.Client/Common/UI/UIScene_MainMenu.h
index 87de602c..07945668 100644
--- a/Minecraft.Client/Common/UI/UIScene_MainMenu.h
+++ b/Minecraft.Client/Common/UI/UIScene_MainMenu.h
@@ -151,8 +151,8 @@ private:
 	static int AuthAddMenuReturned(void *pParam, int iPad, C4JStorage::EMessageResult result);
 	static int AuthKeyboardReturned(LPVOID lpParam, const bool bRes);
 	static int AuthMsFlowReturned(void *pParam, int iPad, C4JStorage::EMessageResult result);
-	static int ElyByUsernameReturned(LPVOID lpParam, const bool bRes);
-	static int ElyByPasswordReturned(LPVOID lpParam, const bool bRes);
+	static int YggdrasilUsernameReturned(LPVOID lpParam, const bool bRes);
+	static int YggdrasilPasswordReturned(LPVOID lpParam, const bool bRes);
 
 	static void LoadTrial();
 
diff --git a/Minecraft.Client/PendingConnection.cpp b/Minecraft.Client/PendingConnection.cpp
index a85e3378..32d59bfa 100644
--- a/Minecraft.Client/PendingConnection.cpp
+++ b/Minecraft.Client/PendingConnection.cpp
@@ -16,7 +16,6 @@
 #include "Settings.h"
 #include "..\Minecraft.World\HandshakeManager.h"
 #include "..\Minecraft.World\SessionAuthModule.h"
-#include "..\Minecraft.World\OfflineAuthModule.h"
 #if defined(_WINDOWS64) && defined(MINECRAFT_SERVER_BUILD)
 #include "..\Minecraft.Server\ServerLogManager.h"
 #include "..\Minecraft.Server\Access\Access.h"
@@ -105,8 +104,14 @@ void PendingConnection::disconnect(DisconnectPacket::eDisconnectReason reason)
 
 void PendingConnection::handlePreLogin(shared_ptr<PreLoginPacket> packet)
 {
-	if (handshakeManager && !authComplete)
+	if (!authComplete)
 	{
+		if (!handshakeManager)
+		{
+			app.DebugPrintf("PendingConnection: PreLogin received without auth handshake, disconnecting\n");
+			disconnect(DisconnectPacket::eDisconnect_AuthFailed);
+			return;
+		}
 		app.DebugPrintf("PendingConnection: PreLogin received before auth complete, disconnecting\n");
 		disconnect(DisconnectPacket::eDisconnect_Closed);
 		return;
@@ -413,10 +418,12 @@ bool PendingConnection::isDisconnected()
 void PendingConnection::initAuth()
 {
 	handshakeManager = new HandshakeManager(true);
-	if (server->authMode == "session")
-		handshakeManager->registerModule(std::make_unique<SessionAuthModule>());
-	else
+	handshakeManager->registerModule(std::make_unique<SessionAuthModule>());
+	if (server->authMode != "session")
+	{
+		handshakeManager->registerModule(std::make_unique<KeypairOfflineAuthModule>());
 		handshakeManager->registerModule(std::make_unique<OfflineAuthModule>());
+	}
 }
 
 void PendingConnection::handleAuth(const shared_ptr<AuthPacket> &packet)
diff --git a/Minecraft.Client/Windows64/Windows64_Minecraft.cpp b/Minecraft.Client/Windows64/Windows64_Minecraft.cpp
index fa5f4ccc..2abaf7c8 100644
--- a/Minecraft.Client/Windows64/Windows64_Minecraft.cpp
+++ b/Minecraft.Client/Windows64/Windows64_Minecraft.cpp
@@ -1296,6 +1296,34 @@ static Minecraft* InitialiseMinecraftRuntime()
 	return pMinecraft;
 }
 
+static LONG WINAPI CrashHandler(EXCEPTION_POINTERS *ep)
+{
+	auto *record = ep->ExceptionRecord;
+	auto *ctx = ep->ContextRecord;
+	HMODULE hMod = GetModuleHandleA(nullptr);
+
+	wchar_t buf[1024];
+	swprintf(buf, 1024,
+		L"Unhandled exception!\n\nCode: 0x%08X\nAddress: 0x%p\nBase: 0x%p\nRVA: 0x%llX\n\nPlease report this crash info.",
+		record->ExceptionCode, record->ExceptionAddress, hMod,
+		(unsigned long long)((char *)record->ExceptionAddress - (char *)hMod));
+
+	FILE *clog = nullptr;
+	if (fopen_s(&clog, "crash.log", "w") == 0 && clog)
+	{
+		fprintf(clog, "[CRASH] Code=0x%08X Addr=0x%p Base=0x%p RVA=0x%llX\n",
+			record->ExceptionCode, record->ExceptionAddress, hMod,
+			(unsigned long long)((char *)record->ExceptionAddress - (char *)hMod));
+		fprintf(clog, "  RIP=0x%llX RSP=0x%llX RBP=0x%llX\n", ctx->Rip, ctx->Rsp, ctx->Rbp);
+		fprintf(clog, "  RAX=0x%llX RBX=0x%llX RCX=0x%llX\n", ctx->Rax, ctx->Rbx, ctx->Rcx);
+		fprintf(clog, "  RDX=0x%llX RSI=0x%llX RDI=0x%llX\n", ctx->Rdx, ctx->Rsi, ctx->Rdi);
+		fclose(clog);
+	}
+
+	MessageBoxW(nullptr, buf, L"MinecraftConsoles Crash", MB_OK | MB_ICONERROR);
+	return EXCEPTION_EXECUTE_HANDLER;
+}
+
 int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
 					   _In_opt_ HINSTANCE hPrevInstance,
 					   _In_ LPTSTR    lpCmdLine,
@@ -1304,6 +1332,8 @@ int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
 	UNREFERENCED_PARAMETER(hPrevInstance);
 	UNREFERENCED_PARAMETER(lpCmdLine);
 
+	SetUnhandledExceptionFilter(CrashHandler);
+
 	// 4J-Win64: set CWD to exe dir so asset paths resolve correctly
 	{
 		char szExeDir[MAX_PATH] = {};
diff --git a/Minecraft.World/AuthModule.h b/Minecraft.World/AuthModule.h
index ae5875b4..308ddcbe 100644
--- a/Minecraft.World/AuthModule.h
+++ b/Minecraft.World/AuthModule.h
@@ -25,3 +25,21 @@ public:
 protected:
 	bool extractIdentity(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername);
 };
+
+class KeypairOfflineAuthModule : public AuthModule
+{
+public:
+	const wchar_t *schemeName() override { return L"mcconsoles:keypair_offline"; }
+	vector<wstring> supportedVariations() override { return {L"rsa2048", L"ed25519"}; }
+	vector<pair<wstring, wstring>> getSettings(const wstring &variation) override { return {{L"key_type", variation}}; }
+	bool onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername) override { return extractIdentity(fields, outUid, outUsername); }
+};
+
+class OfflineAuthModule : public AuthModule
+{
+public:
+	const wchar_t *schemeName() override { return L"mcconsoles:offline"; }
+	vector<wstring> supportedVariations() override { return {}; }
+	vector<pair<wstring, wstring>> getSettings(const wstring &) override { return {}; }
+	bool onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername) override { return extractIdentity(fields, outUid, outUsername); }
+};
diff --git a/Minecraft.World/HandshakeManager.cpp b/Minecraft.World/HandshakeManager.cpp
index 96d83b26..8ccc4b04 100644
--- a/Minecraft.World/HandshakeManager.cpp
+++ b/Minecraft.World/HandshakeManager.cpp
@@ -48,7 +48,16 @@ shared_ptr<AuthPacket> HandshakeManager::handlePacket(const shared_ptr<AuthPacke
 shared_ptr<AuthPacket> HandshakeManager::createInitialPacket()
 {
 	state = HandshakeState::VERSION_SENT;
-	return makePacket(AuthStage::ANNOUNCE_VERSION, {{L"version", PROTOCOL_VERSION}});
+	wstring schemes;
+	for (const auto &[name, mod] : modules)
+	{
+		if (!schemes.empty()) schemes += L",";
+		schemes += name;
+	}
+	return makePacket(AuthStage::ANNOUNCE_VERSION, {
+		{L"version", PROTOCOL_VERSION},
+		{L"schemes", schemes}
+	});
 }
 
 shared_ptr<AuthPacket> HandshakeManager::handleServer(const shared_ptr<AuthPacket> &packet)
@@ -61,11 +70,32 @@ shared_ptr<AuthPacket> HandshakeManager::handleServer(const shared_ptr<AuthPacke
 		if (protocolVersion != PROTOCOL_VERSION)
 			return fail();
 
-		// Pick first registered module as the scheme
 		if (modules.empty())
 			return fail();
 
-		activeModule = modules.begin()->second.get();
+		auto splitCsv = [](const wstring &s) {
+			vector<wstring> out;
+			for (size_t p = 0; p < s.size(); ) {
+				size_t c = s.find(L',', p);
+				if (c == wstring::npos) c = s.size();
+				out.push_back(s.substr(p, c - p));
+				p = c + 1;
+			}
+			return out;
+		};
+		auto supported = splitCsv(getField(packet->fields, L"schemes"));
+
+		activeModule = nullptr;
+		for (auto &[name, mod] : modules)
+		{
+			if (supported.empty() || std::find(supported.begin(), supported.end(), name) != supported.end())
+			{
+				activeModule = mod.get();
+				break;
+			}
+		}
+		if (!activeModule)
+			return fail();
 		state = HandshakeState::SCHEME_DECLARED;
 		return makePacket(AuthStage::DECLARE_SCHEME, {
 			{L"version", PROTOCOL_VERSION},
@@ -133,6 +163,8 @@ shared_ptr<AuthPacket> HandshakeManager::handleClient(const shared_ptr<AuthPacke
 		protocolVersion = getField(packet->fields, L"version");
 		wstring scheme = getField(packet->fields, L"scheme");
 
+		app.DebugPrintf("AUTH CLIENT: DECLARE_SCHEME scheme=%ls\n", scheme.c_str());
+
 		if (protocolVersion != PROTOCOL_VERSION)
 			return fail();
 
@@ -149,24 +181,39 @@ shared_ptr<AuthPacket> HandshakeManager::handleClient(const shared_ptr<AuthPacke
 		else
 			activeVariation = variations.empty() ? L"" : variations[0];
 
+		app.DebugPrintf("AUTH CLIENT: accepting variation=%ls\n", activeVariation.c_str());
 		state = HandshakeState::SCHEME_ACCEPTED;
 		return makePacket(AuthStage::ACCEPT_SCHEME, {{L"variation", activeVariation}});
 	}
 
 	case AuthStage::SCHEME_SETTINGS:
 	{
+		if (!activeModule)
+			return fail();
 		wstring serverId = getField(packet->fields, L"serverId");
-		wstring sessionEndpoint = getField(packet->fields, L"sessionEndpoint");
+		wstring joinUrlW = getField(packet->fields, L"joinUrl");
 		wstring scheme(activeModule->schemeName());
-		if (scheme == L"mcconsoles:session" && !accessToken.empty())
+
+		app.DebugPrintf("AUTH CLIENT: SCHEME_SETTINGS joinUrl=%ls serverId=%ls\n", joinUrlW.c_str(), serverId.c_str());
+
+		if (scheme == L"mcconsoles:session" && !accessToken.empty() && !joinUrlW.empty())
 		{
 			nlohmann::json body = {
 				{"accessToken", narrowStr(accessToken)},
 				{"selectedProfile", narrowStr(clientUid)},
 				{"serverId", narrowStr(serverId)}
 			};
-			auto resp = HttpClient::post(narrowStr(sessionEndpoint) + "/session/minecraft/join", body.dump());
-			if (resp.statusCode != 204)
+			string joinUrl = narrowStr(joinUrlW);
+			app.DebugPrintf("AUTH CLIENT: POSTing join to %s\n", joinUrl.c_str());
+			HttpResponse resp;
+			try {
+				resp = HttpClient::post(joinUrl, body.dump());
+			} catch (...) {
+				app.DebugPrintf("AUTH CLIENT: join POST threw exception\n");
+				return fail();
+			}
+			app.DebugPrintf("AUTH CLIENT: join POST status=%d\n", resp.statusCode);
+			if (resp.statusCode < 200 || resp.statusCode >= 300)
 				return fail();
 		}
 
diff --git a/Minecraft.World/MapItem.cpp b/Minecraft.World/MapItem.cpp
index 61c203e3..3ff8206c 100644
--- a/Minecraft.World/MapItem.cpp
+++ b/Minecraft.World/MapItem.cpp
@@ -21,6 +21,7 @@ MapItem::MapItem(int id) : ComplexItem(id)
 
 shared_ptr<MapItemSavedData> MapItem::getSavedData(short idNum, Level *level)
 {
+	if (!level) return nullptr;
 	std::wstring id = wstring( L"map_" ) + std::to_wstring(idNum);
 	shared_ptr<MapItemSavedData> mapItemSavedData = dynamic_pointer_cast<MapItemSavedData>(level->getSavedData(typeid(MapItemSavedData), id));
 
@@ -42,6 +43,7 @@ shared_ptr<MapItemSavedData> MapItem::getSavedData(short idNum, Level *level)
 
 shared_ptr<MapItemSavedData> MapItem::getSavedData(shared_ptr<ItemInstance> itemInstance, Level *level)
 {
+	if (!level) return nullptr;
 	MemSect(31);
 	std::wstring id = wstring( L"map_" ) + std::to_wstring(itemInstance->getAuxValue() );
 	MemSect(0);
@@ -254,6 +256,7 @@ void MapItem::update(Level *level, shared_ptr<Entity> player, shared_ptr<MapItem
 
 void MapItem::inventoryTick(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Entity> owner, int slot, bool selected)
 {
+	if (!level) return;
 	if (level->isClientSide) return;
 
 	shared_ptr<MapItemSavedData> data = getSavedData(itemInstance, level);
@@ -293,7 +296,10 @@ void MapItem::inventoryTick(shared_ptr<ItemInstance> itemInstance, Level *level,
 
 shared_ptr<Packet> MapItem::getUpdatePacket(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Player> player)
 {
-	charArray data = MapItem::getSavedData(itemInstance, level)->getUpdatePacket(itemInstance, level, player);
+	if (!level) return nullptr;
+	auto savedData = MapItem::getSavedData(itemInstance, level);
+	if (!savedData) return nullptr;
+	charArray data = savedData->getUpdatePacket(itemInstance, level, player);
 
 	if (data.data == nullptr || data.length == 0) return nullptr;
 
@@ -304,6 +310,7 @@ shared_ptr<Packet> MapItem::getUpdatePacket(shared_ptr<ItemInstance> itemInstanc
 
 void MapItem::onCraftedBy(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Player> player)
 {
+	if (!level) return;
 	wchar_t buf[64];
 
 	int mapScale = 3;
diff --git a/Minecraft.World/OfflineAuthModule.cpp b/Minecraft.World/OfflineAuthModule.cpp
deleted file mode 100644
index 5369ceac..00000000
--- a/Minecraft.World/OfflineAuthModule.cpp
+++ /dev/null
@@ -1,36 +0,0 @@
-#include "stdafx.h"
-#include "OfflineAuthModule.h"
-
-const wchar_t *KeypairOfflineAuthModule::schemeName() { return L"mcconsoles:keypair_offline"; }
-
-vector<wstring> KeypairOfflineAuthModule::supportedVariations()
-{
-	return {L"rsa2048", L"ed25519"};
-}
-
-vector<pair<wstring, wstring>> KeypairOfflineAuthModule::getSettings(const wstring &variation)
-{
-	return {{L"key_type", variation}};
-}
-
-bool KeypairOfflineAuthModule::onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername)
-{
-	return extractIdentity(fields, outUid, outUsername);
-}
-
-const wchar_t *OfflineAuthModule::schemeName() { return L"mcconsoles:offline"; }
-
-vector<wstring> OfflineAuthModule::supportedVariations()
-{
-	return {};
-}
-
-vector<pair<wstring, wstring>> OfflineAuthModule::getSettings(const wstring &variation)
-{
-	return {};
-}
-
-bool OfflineAuthModule::onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername)
-{
-	return extractIdentity(fields, outUid, outUsername);
-}
diff --git a/Minecraft.World/OfflineAuthModule.h b/Minecraft.World/OfflineAuthModule.h
deleted file mode 100644
index b2b4454d..00000000
--- a/Minecraft.World/OfflineAuthModule.h
+++ /dev/null
@@ -1,22 +0,0 @@
-#pragma once
-using namespace std;
-
-#include "AuthModule.h"
-
-class KeypairOfflineAuthModule : public AuthModule
-{
-public:
-	const wchar_t *schemeName() override;
-	vector<wstring> supportedVariations() override;
-	vector<pair<wstring, wstring>> getSettings(const wstring &variation) override;
-	bool onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername) override;
-};
-
-class OfflineAuthModule : public AuthModule
-{
-public:
-	const wchar_t *schemeName() override;
-	vector<wstring> supportedVariations() override;
-	vector<pair<wstring, wstring>> getSettings(const wstring &variation) override;
-	bool onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername) override;
-};
diff --git a/Minecraft.World/SessionAuthModule.cpp b/Minecraft.World/SessionAuthModule.cpp
index 50844b39..5f100aba 100644
--- a/Minecraft.World/SessionAuthModule.cpp
+++ b/Minecraft.World/SessionAuthModule.cpp
@@ -4,6 +4,8 @@
 #include "StringHelpers.h"
 #include "Common/vendor/nlohmann/json.hpp"
 #include <random>
+#include <fstream>
+#include <algorithm>
 
 static wstring generateServerId()
 {
@@ -14,50 +16,96 @@ static wstring generateServerId()
 	return id;
 }
 
-SessionAuthModule::SessionAuthModule()
+static vector<YggdrasilProviderConfig> s_registryProviders;
+static bool s_registryLoaded = false;
+
+void YggdrasilRegistry::load()
 {
-	endpoints[L"mojang"] = {L"https://authserver.mojang.com", L"https://sessionserver.mojang.com"};
-	endpoints[L"elyby"] = {L"https://authserver.ely.by", L"https://authserver.ely.by"};
+	s_registryProviders.clear();
+
+	std::ifstream file("yggdrasil.json");
+	if (file.is_open())
+	{
+		auto j = nlohmann::json::parse(file, nullptr, false);
+		if (j.is_array())
+		{
+			for (const auto &entry : j)
+			{
+				if (!entry.is_object()) continue;
+				YggdrasilProviderConfig cfg;
+				cfg.name = convStringToWstring(entry.value("name", ""));
+				cfg.displayName = convStringToWstring(entry.value("displayName", ""));
+				cfg.authUrl = entry.value("authUrl", "");
+				cfg.sessionUrl = entry.value("sessionUrl", "");
+				if (!cfg.name.empty() && !cfg.sessionUrl.empty())
+					s_registryProviders.push_back(std::move(cfg));
+			}
+		}
+	}
+
+	if (std::none_of(s_registryProviders.begin(), s_registryProviders.end(),
+		[](const auto &p) { return p.name == L"elyby"; }))
+		s_registryProviders.insert(s_registryProviders.begin(),
+			{L"elyby", L"Ely.by", "https://authserver.ely.by/auth", "https://authserver.ely.by/session"});
+
+	s_registryProviders.push_back(
+		{L"mojang", L"Mojang", "", "https://sessionserver.mojang.com/session/minecraft"});
+
+	s_registryLoaded = true;
+}
+
+const vector<YggdrasilProviderConfig> &YggdrasilRegistry::providers()
+{
+	if (!s_registryLoaded) load();
+	return s_registryProviders;
+}
+
+const YggdrasilProviderConfig *YggdrasilRegistry::find(const wstring &name)
+{
+	for (const auto &p : providers())
+		if (p.name == name) return &p;
+	return nullptr;
+}
+
+const YggdrasilProviderConfig &YggdrasilRegistry::defaultProvider()
+{
+	const auto &list = providers();
+	for (const auto &p : list)
+		if (p.name != L"mojang") return p;
+	return list[0];
 }
 
 const wchar_t *SessionAuthModule::schemeName() { return L"mcconsoles:session"; }
 
 vector<wstring> SessionAuthModule::supportedVariations()
 {
-	return {L"mojang", L"elyby"};
+	vector<wstring> result;
+	for (const auto &p : YggdrasilRegistry::providers())
+		result.push_back(p.name);
+	return result;
 }
 
 vector<pair<wstring, wstring>> SessionAuthModule::getSettings(const wstring &variation)
 {
-	auto it = endpoints.find(variation);
-	if (it == endpoints.end()) return {};
+	auto *p = YggdrasilRegistry::find(variation);
+	if (!p) return {};
 
-	activeSessionEndpoint = it->second.sessionEndpoint;
+	activeProvider = p;
 	activeServerId = generateServerId();
-
 	return {
-		{L"authEndpoint", it->second.authEndpoint},
-		{L"sessionEndpoint", it->second.sessionEndpoint},
+		{L"joinUrl", convStringToWstring(p->joinUrl())},
 		{L"serverId", activeServerId}
 	};
 }
 
-bool SessionAuthModule::onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername)
+bool SessionAuthModule::serverVerify(const YggdrasilProviderConfig &provider, const wstring &username, const wstring &serverId, wstring &outUid, wstring &outUsername)
 {
-	wstring username;
-	for (const auto &[k, v] : fields)
-	{
-		if (k == L"username") username = v;
-	}
-
-	if (username.empty() || activeServerId.empty() || activeSessionEndpoint.empty())
-		return false;
-
-	string url = narrowStr(activeSessionEndpoint)
-		+ "/session/minecraft/hasJoined?username=" + narrowStr(username)
-		+ "&serverId=" + narrowStr(activeServerId);
+	string url = provider.hasJoinedUrl() + "?username=" + narrowStr(username) + "&serverId=" + narrowStr(serverId);
 
+	app.DebugPrintf("AUTH SERVER [%ls]: hasJoined GET %s\n", provider.name.c_str(), url.c_str());
 	auto response = HttpClient::get(url);
+	app.DebugPrintf("AUTH SERVER [%ls]: hasJoined status=%d\n", provider.name.c_str(), response.statusCode);
+
 	if (response.statusCode != 200)
 		return false;
 
@@ -67,12 +115,25 @@ bool SessionAuthModule::onAuthData(const vector<pair<wstring, wstring>> &fields,
 
 	string id = json.value("id", "");
 	string name = json.value("name", "");
-
 	if (id.empty() || name.empty())
 		return false;
 
 	outUid = convStringToWstring(id);
 	outUsername = convStringToWstring(name);
+	return true;
+}
+
+bool SessionAuthModule::onAuthData(const vector<pair<wstring, wstring>> &fields, wstring &outUid, wstring &outUsername)
+{
+	wstring username;
+	for (const auto &[k, v] : fields)
+		if (k == L"username") username = v;
+
+	if (username.empty() || activeServerId.empty() || !activeProvider)
+		return false;
+
+	if (!serverVerify(*activeProvider, username, activeServerId, outUid, outUsername))
+		return false;
 
 	return validate(outUid, outUsername);
 }
diff --git a/Minecraft.World/SessionAuthModule.h b/Minecraft.World/SessionAuthModule.h
index ecb60c06..2990edbd 100644
--- a/Minecraft.World/SessionAuthModule.h
+++ b/Minecraft.World/SessionAuthModule.h
@@ -1,24 +1,41 @@
 #pragma once
 using namespace std;
-
 #include "AuthModule.h"
-#include <unordered_map>
+#include <vector>
+#include <memory>
+
+struct YggdrasilProviderConfig
+{
+	wstring name;
+	wstring displayName;
+	string authUrl;
+	string sessionUrl;
+	string authenticateUrl() const { return authUrl + "/authenticate"; }
+	string validateUrl()     const { return authUrl + "/validate"; }
+	string refreshUrl()      const { return authUrl + "/refresh"; }
+	string joinUrl()         const { return sessionUrl + "/join"; }
+	string hasJoinedUrl()    const { return sessionUrl + "/hasJoined"; }
+};
+
+class YggdrasilRegistry
+{
+public:
+	static void load();
+	static const vector<YggdrasilProviderConfig> &providers();
+	static const YggdrasilProviderConfig *find(const wstring &name);
+	static const YggdrasilProviderConfig &defaultProvider();
+};
 
 class SessionAuthModule : public AuthModule
 {
-public:
-	struct EndpointPair {
-		wstring authEndpoint;
-		wstring sessionEndpoint;
-	};
-
 private:
-	unordered_map<wstring, EndpointPair> endpoints;
-	wstring activeSessionEndpoint;
+	const YggdrasilProviderConfig *activeProvider = nullptr;
 	wstring activeServerId;
 
+	bool serverVerify(const YggdrasilProviderConfig &provider, const wstring &username, const wstring &serverId, wstring &outUid, wstring &outUsername);
+
 public:
-	SessionAuthModule();
+	SessionAuthModule() = default;
 
 	const wchar_t *schemeName() override;
 	vector<wstring> supportedVariations() override;
diff --git a/Minecraft.World/cmake/sources/Common.cmake b/Minecraft.World/cmake/sources/Common.cmake
index 8bf351e9..dc843f13 100644
--- a/Minecraft.World/cmake/sources/Common.cmake
+++ b/Minecraft.World/cmake/sources/Common.cmake
@@ -263,8 +263,6 @@ set(_MINECRAFT_WORLD_COMMON_NET_MINECRAFT_NETWORK_PACKET
   "${CMAKE_CURRENT_SOURCE_DIR}/AuthModule.h"
   "${CMAKE_CURRENT_SOURCE_DIR}/SessionAuthModule.cpp"
   "${CMAKE_CURRENT_SOURCE_DIR}/SessionAuthModule.h"
-  "${CMAKE_CURRENT_SOURCE_DIR}/OfflineAuthModule.cpp"
-  "${CMAKE_CURRENT_SOURCE_DIR}/OfflineAuthModule.h"
   "${CMAKE_CURRENT_SOURCE_DIR}/AuthPackets.cpp"
   "${CMAKE_CURRENT_SOURCE_DIR}/AuthPackets.h"
   "${CMAKE_CURRENT_SOURCE_DIR}/UUID.cpp"
diff --git a/yggdrasil.json b/yggdrasil.json
new file mode 100644
index 00000000..4fbd9549
--- /dev/null
+++ b/yggdrasil.json
@@ -0,0 +1,8 @@
+[
+    {
+        "name": "elyby",
+        "displayName": "Ely.by",
+        "authUrl": "https://authserver.ely.by/auth",
+        "sessionUrl": "https://authserver.ely.by/session"
+    }
+]