refactored the credential checking logic into a shared helper function to reduce code duplication

auth/google_auth.py

@@ -232,6 +232,19 @@ def load_client_secrets(client_secrets_path: str) -> Dict[str, Any]:
     except (IOError, json.JSONDecodeError) as e:
         logger.error(f"Error loading client secrets file {client_secrets_path}: {e}")
         raise
+def check_client_secrets() -> Optional[str]:
+    """
+    Checks for the presence of OAuth client secrets, either as environment
+    variables or as a file.
+
+    Returns:
+        An error message string if secrets are not found, otherwise None.
+    """
+    env_config = load_client_secrets_from_env()
+    if not env_config and not os.path.exists(CONFIG_CLIENT_SECRETS_PATH):
+        logger.error(f"OAuth client credentials not found. No environment variables set and no file at {CONFIG_CLIENT_SECRETS_PATH}")
+        return "OAuth client credentials not found. Please set GOOGLE_OAUTH_CLIENT_ID and GOOGLE_OAUTH_CLIENT_SECRET environment variables or provide client_secret.json file."
+    return None
 
 def create_oauth_flow(scopes: List[str], redirect_uri: str, state: Optional[str] = None) -> Flow:
     """Creates an OAuth flow using environment variables or client secrets file."""