fix(auth): prevent duplicate iflow BXAuth tokens

internal/auth/iflow/cookie_helpers.go

@@ -1,7 +1,10 @@
 package iflow
 
 import (
+	"encoding/json"
 	"fmt"
+	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -36,3 +39,61 @@ func SanitizeIFlowFileName(raw string) string {
 	}
 	return strings.TrimSpace(result.String())
 }
+
+// ExtractBXAuth extracts the BXAuth value from a cookie string.
+func ExtractBXAuth(cookie string) string {
+	parts := strings.Split(cookie, ";")
+	for _, part := range parts {
+		part = strings.TrimSpace(part)
+		if strings.HasPrefix(part, "BXAuth=") {
+			return strings.TrimPrefix(part, "BXAuth=")
+		}
+	}
+	return ""
+}
+
+// CheckDuplicateBXAuth checks if the given BXAuth value already exists in any iflow auth file.
+// Returns the path of the existing file if found, empty string otherwise.
+func CheckDuplicateBXAuth(authDir, bxAuth string) (string, error) {
+	if bxAuth == "" {
+		return "", nil
+	}
+
+	entries, err := os.ReadDir(authDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return "", nil
+		}
+		return "", fmt.Errorf("read auth dir failed: %w", err)
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		name := entry.Name()
+		if !strings.HasPrefix(name, "iflow-") || !strings.HasSuffix(name, ".json") {
+			continue
+		}
+
+		filePath := filepath.Join(authDir, name)
+		data, err := os.ReadFile(filePath)
+		if err != nil {
+			continue
+		}
+
+		var tokenData struct {
+			Cookie string `json:"cookie"`
+		}
+		if err := json.Unmarshal(data, &tokenData); err != nil {
+			continue
+		}
+
+		existingBXAuth := ExtractBXAuth(tokenData.Cookie)
+		if existingBXAuth != "" && existingBXAuth == bxAuth {
+			return filePath, nil
+		}
+	}
+
+	return "", nil
+}