def cognito_idp_user_pool_arn(self, lookup, default=None):
    """
    Args:
        lookup: Cognito User Pool name, proto0-cms-user-pool
        default: the optional value to return if lookup failed; returns None if not set

    Returns:
        the User Pool ARN corresponding to the given lookup, else default/None
    """
    client = EFAwsResolver.__CLIENTS["cognito-idp"]
    user_pool_id = self.cognito_idp_user_pool_id(lookup, default)
    if user_pool_id == default:
      return default

    response = client.describe_user_pool(UserPoolId=user_pool_id)

    if not response.has_key("UserPool"):
      return default

    return response["UserPool"]["Arn"]