diff --git a/backend/internal/errors/codes.go b/backend/internal/errors/codes.go
index 739cfdb..9417209 100644
--- a/backend/internal/errors/codes.go
+++ b/backend/internal/errors/codes.go
@@ -14,6 +14,12 @@ const (
 	CodeSTTError        = "STT_ERROR"
 	CodeTTSError        = "TTS_ERROR"
 	CodeInternalError   = "INTERNAL_ERROR"
+
+	// 认证相关错误码
+	CodeUsernameTaken      = "USERNAME_TAKEN"
+	CodeInvalidCredentials = "INVALID_CREDENTIALS"
+	CodeInvalidToken       = "INVALID_TOKEN"
+	CodeInvalidInput       = "INVALID_INPUT"
 )
 
 // Sender 定义发送 WS 错误消息的接口，便于测试 mock。