diff --git a/LaunchServer/source/auth/handler/AuthHandler.java b/LaunchServer/source/auth/handler/AuthHandler.java
index 13bb445..bd0dd51 100644
--- a/LaunchServer/source/auth/handler/AuthHandler.java
+++ b/LaunchServer/source/auth/handler/AuthHandler.java
@@ -11,6 +11,7 @@
 import launcher.helper.VerifyHelper;
 import launcher.serialize.config.ConfigObject;
 import launcher.serialize.config.entry.BlockConfigEntry;
+import launchserver.auth.AuthException;
 
 public abstract class AuthHandler extends ConfigObject implements Flushable {
 	private static final Map<String, Adapter<AuthHandler>> AUTH_HANDLERS = new ConcurrentHashMap<>(4);
@@ -36,6 +37,11 @@
 	public abstract String uuidToUsername(UUID uuid) throws IOException;
 
 	@LauncherAPI
+	public static UUID authError(String message) throws AuthException {
+		throw new AuthException(message);
+	}
+
+	@LauncherAPI
 	public static AuthHandler newHandler(String name, BlockConfigEntry block) {
 		Adapter<AuthHandler> authHandlerAdapter = VerifyHelper.getMapValue(AUTH_HANDLERS, name,
 			String.format("Unknown auth handler: '%s'", name));
diff --git a/LaunchServer/source/auth/handler/CachedAuthHandler.java b/LaunchServer/source/auth/handler/CachedAuthHandler.java
index cd76a83..7d425dd 100644
--- a/LaunchServer/source/auth/handler/CachedAuthHandler.java
+++ b/LaunchServer/source/auth/handler/CachedAuthHandler.java
@@ -26,7 +26,7 @@
 	public final synchronized UUID auth(String username, String accessToken) throws IOException {
 		Entry entry = getEntry(username);
 		if (entry == null || !updateAuth(entry.uuid, entry.username, accessToken)) {
-			return null; // Account doesn't exist
+			return authError(String.format("Account doesn't exist: '%s'", username));
 		}
 
 		// Update cached access token (and username case)
diff --git a/LaunchServer/source/response/Response.java b/LaunchServer/source/response/Response.java
index 9650693..a493590 100644
--- a/LaunchServer/source/response/Response.java
+++ b/LaunchServer/source/response/Response.java
@@ -4,6 +4,7 @@
 
 import launcher.LauncherAPI;
 import launcher.helper.LogHelper;
+import launcher.request.RequestException;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
 import launchserver.LaunchServer;
@@ -40,6 +41,11 @@
 		output.writeString("", 0);
 	}
 
+	@LauncherAPI
+	public static void requestError(String message) throws RequestException {
+		throw new RequestException(message);
+	}
+
 	@FunctionalInterface
 	public interface Factory {
 		@LauncherAPI
diff --git a/LaunchServer/source/response/auth/AuthResponse.java b/LaunchServer/source/response/auth/AuthResponse.java
index dc31b0f..38c6596 100644
--- a/LaunchServer/source/response/auth/AuthResponse.java
+++ b/LaunchServer/source/response/auth/AuthResponse.java
@@ -9,11 +9,11 @@
 import launcher.helper.LogHelper;
 import launcher.helper.SecurityHelper;
 import launcher.helper.VerifyHelper;
-import launcher.request.RequestException;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
 import launchserver.LaunchServer;
 import launchserver.auth.AuthException;
+import launchserver.auth.provider.AuthProvider;
 import launchserver.response.Response;
 import launchserver.response.profile.ProfileByUUIDResponse;
 
@@ -33,7 +33,8 @@
 			password = IOHelper.decode(SecurityHelper.newRSADecryptCipher(server.privateKey).
 				doFinal(encryptedPassword));
 		} catch (IllegalBlockSizeException | BadPaddingException ignored) {
-			throw new RequestException("Password decryption error");
+			requestError("Password decryption error");
+			return;
 		}
 
 		// Authenticate
@@ -42,21 +43,26 @@
 		try {
 			username = server.config.authProvider.auth(login, password);
 			if (!VerifyHelper.isValidUsername(username)) {
-				throw new AuthException(String.format("Illegal username: '%s'", username));
+				AuthProvider.authError(String.format("Illegal username: '%s'", username));
 			}
 		} catch (AuthException e) {
-			throw new RequestException(e);
+			requestError(e.getMessage());
+			return;
 		} catch (Exception e) {
 			LogHelper.error(e);
-			throw new RequestException("Internal auth error", e);
+			requestError("Internal auth error");
+			return;
 		}
 		debug("Auth: '%s' -> '%s'", login, username);
 
 		// Authenticate on server (and get UUID)
 		String accessToken = SecurityHelper.randomStringToken();
-		UUID uuid = server.config.authHandler.auth(username, accessToken);
-		if (uuid == null) {
-			throw new RequestException("Can't assign UUID");
+		UUID uuid;
+		try {
+			uuid =server.config.authHandler.auth(username, accessToken);
+		} catch (AuthException e) {
+			requestError(e.getMessage());
+			return;
 		}
 		writeNoError(output);
 
diff --git a/LaunchServer/source/response/update/LauncherResponse.java b/LaunchServer/source/response/update/LauncherResponse.java
index fa73bc4..13a2be0 100644
--- a/LaunchServer/source/response/update/LauncherResponse.java
+++ b/LaunchServer/source/response/update/LauncherResponse.java
@@ -5,7 +5,6 @@
 
 import launcher.client.ClientProfile;
 import launcher.helper.SecurityHelper;
-import launcher.request.RequestException;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
 import launcher.serialize.signed.SignedBytesHolder;
@@ -23,7 +22,8 @@
 		// Resolve launcher binary
 		SignedBytesHolder bytes = (input.readBoolean() ? server.launcherEXEBinary : server.launcherBinary).getBytes();
 		if (bytes == null) {
-			throw new RequestException("Missing launcher binary");
+			requestError("Missing launcher binary");
+			return;
 		}
 		writeNoError(output);
 
diff --git a/LaunchServer/source/response/update/UpdateResponse.java b/LaunchServer/source/response/update/UpdateResponse.java
index 3e86387..cebf47a 100644
--- a/LaunchServer/source/response/update/UpdateResponse.java
+++ b/LaunchServer/source/response/update/UpdateResponse.java
@@ -9,7 +9,6 @@
 import launcher.hasher.HashedDir;
 import launcher.hasher.HashedEntry;
 import launcher.helper.IOHelper;
-import launcher.request.RequestException;
 import launcher.request.update.UpdateRequest;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
@@ -28,7 +27,8 @@
 		String updateDirName = IOHelper.verifyFileName(input.readString(255));
 		SignedObjectHolder<HashedDir> hdir = server.getUpdateDir(updateDirName);
 		if (hdir == null) {
-			throw new RequestException(String.format("Unknown update dir: %s", updateDirName));
+			requestError(String.format("Unknown update dir: %s", updateDirName));
+			return;
 		}
 		writeNoError(output);