Update auth_helpers.py

Author: vgvoleg

ydb/auth_helpers.py

@@ -9,6 +9,7 @@ def read_bytes(f):
 
 
 def load_ydb_root_certificate(path: Optional[str] = None):
+    path = path if path is not None else os.getenv("YDB_SSL_ROOT_CERTIFICATES_FILE", None)
     if path is not None and os.path.exists(path):
         return read_bytes(path)
     return None