code: def restore_existing_iam_env_vars(self):
          
          for i in ['AWS_ACCESS_KEY_ID', 'AWS_SECRET_ACCESS_KEY',
                    'AWS_SESSION_TOKEN']:
              if 'OLD_' + i in self.env_vars:
                  self.env_vars[i] = self.env_vars['OLD_' + i]
              elif i in self.env_vars:
                  self.env_vars.pop(i)
docs: Restore backed up IAM environment variables.