如何设置访问AWS DynamoDB所需的身份验证

Question

首先，我只需按照给定的指令访问DynamoDB， 之后，我构建了名为 DynamoDBObjectMapper-Sample 的下载示例项目，我收到了错误日志 -

错误：错误Domain = com.amazonaws.AWSCognitoIdentityErrorDomain Code = 8“（null）”UserInfo = {__ type = NotAuthorizedException，message =此身份池不支持未经身份验证的访问。}

执行以下代码后打印此错误 -

        UIApplication.shared.isNetworkActivityIndicatorVisible = true

        let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
        let queryExpression = AWSDynamoDBScanExpression()
        queryExpression.exclusiveStartKey = self.lastEvaluatedKey
        queryExpression.limit = 20
        dynamoDBObjectMapper.scan(DDBTableRow.self, expression: queryExpression).continueWith(executor: AWSExecutor.mainThread(), block: { (task:AWSTask!) -> AnyObject! in

            if self.lastEvaluatedKey == nil {
                self.tableRows?.removeAll(keepingCapacity: true)
            }

            if let paginatedOutput = task.result {
                for item in paginatedOutput.items as! [DDBTableRow] {
                    self.tableRows?.append(item)
                }

                self.lastEvaluatedKey = paginatedOutput.lastEvaluatedKey
                if paginatedOutput.lastEvaluatedKey == nil {
                    self.doneLoading = true
                }
            }

            UIApplication.shared.isNetworkActivityIndicatorVisible = false
            self.tableView.reloadData()

            if let error = task.error as NSError? {
                print("Error: \(error)")
            }

            return nil
        })

所以请帮我设置身份验证密钥 -