code: def discard(self, timeout=None, metadata=None, credentials=None):
          
          if not self._common_discard():
              return
  
          new_metadata = self._dg.add_login_metadata(metadata)
          try:
              self._dc.commit_or_abort(self._ctx, timeout=timeout,
                                       metadata=new_metadata,
                                       credentials=credentials)
          except Exception as error:
              if util.is_jwt_expired(error):
                  self._dg.retry_login()
                  new_metadata = self._dg.add_login_metadata(metadata)
                  self._dc.commit_or_abort(self._ctx, timeout=timeout,
                                           metadata=new_metadata,
                                           credentials=credentials)
              else:
                  raise error
docs: Discards the transaction.