feat/auth-hook: add post auth hook

sdk/auth/filestore.go

@@ -62,8 +62,16 @@ func (s *FileTokenStore) Save(ctx context.Context, auth *cliproxyauth.Auth) (str
 		return "", fmt.Errorf("auth filestore: create dir failed: %w", err)
 	}
 
+	// metadataSetter is a private interface for TokenStorage implementations that support metadata injection.
+	type metadataSetter interface {
+		SetMetadata(map[string]any)
+	}
+
 	switch {
 	case auth.Storage != nil:
+		if setter, ok := auth.Storage.(metadataSetter); ok {
+			setter.SetMetadata(auth.Metadata)
+		}
 		if err = auth.Storage.SaveTokenToFile(path); err != nil {
 			return "", err
 		}