如何通过swift中经过身份验证的cognito用户（用户池）访问DynamoDB

我正在尝试将AWS Cognito（用户池）和AWS DynamoDB用于我的移动应用程序 .

我做了以下事情：

• 在AWS Cognito上创建用户池 .

• 在AWS Cognito上创建标识池，并在身份验证提供程序上将用户池标识，应用程序客户机标识设置为Cognito .

• 在AWS DynamoDB上创建SampleTable .

• 设置权限经过身份验证的角色以在AWS IAM上访问SampleTable .

我创建了这段代码：

let userPoolConfigration = AWSServiceConfiguration.init(region: AWSRegionType.USEast1, credentialsProvider: nil)
AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = userPoolConfigration

let userServiceConfigration = AWSCognitoIdentityUserPoolConfiguration.init(clientId: "(client id from user pool)", clientSecret: "(client secret from user pool)", poolId: "(user pool id from user pool)")

AWSCognitoIdentityUserPool.registerCognitoIdentityUserPoolWithUserPoolConfiguration(userServiceConfigration, forKey: "AmazonCognitoIdentityProvider")
let pool = AWSCognitoIdentityUserPool(forKey: "AmazonCognitoIdentityProvider")

    let user = pool.getUser("sampleuser")
    user.getSession("sampleuser", password: "samplepassword", validationData: nil, scopes: nil).continueWithBlock({ task in
        if (task.error == nil) {
            let credentialsProvider = AWSCognitoCredentialsProvider(regionType:.USEast1,
                identityPoolId:"(identity id from identity pool)")

            let ret = task.result as! AWSCognitoIdentityUserSession
            let logins: NSDictionary = NSDictionary(dictionary: ["cognito-idp.us-east-1.amazonaws.com/(user pool id from user pool)" : ret.idToken!.tokenString])
            credentialsProvider.logins = logins as [NSObject : AnyObject]
            let configuration = AWSServiceConfiguration(region: .USEast1, credentialsProvider: credentialsProvider)
            AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = configuration
            credentialsProvider.clearKeychain()
            credentialsProvider.credentials().continueWithBlock {(task: AWSTask!) -> AnyObject! in
                let result = task.result as! AWSCredentials
                let newcredentialsProvider = AWSStaticCredentialsProvider(accessKey:result.accessKey, secretKey: result.secretKey)
                let newdefaultServiceConfiguration = AWSServiceConfiguration(region: .USEast1, credentialsProvider: newcredentialsProvider)
                AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = newdefaultServiceConfiguration

                let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.defaultDynamoDBObjectMapper()
                let scanExpression = AWSDynamoDBScanExpression()

                dynamoDBObjectMapper.scan(SampleTable.self, expression: scanExpression).continueWithBlock({ task in
                    print(task.result)
                    return nil
                })
                return nil
            }
        }
        return nil
    })

但是当运行“dynamoDBObjectMapper.scan（）”时出现了这个错误：

2016-06-23 16:57:04.988 AWSiOSSDK v2.4.3 [Debug] AWSURLSessionManager.m line:525 | -[AWSURLSessionManager printHTTPHeadersAndBodyForRequest:] | Request headers:
{
    "Content-Type" = "application/x-amz-json-1.0";
    Host = "dynamodb.us-east-1.amazonaws.com";
    "User-Agent" = "aws-sdk-iOS/2.4.3 iPhone-OS/9.2 en_US mapper";
    "X-Amz-Date" = 20160623T075704Z;
    "X-Amz-Target" = "DynamoDB_20120810.Scan";
}
2016-06-23 16:57:04.988 if-she[3704:367618] AWSiOSSDK v2.4.3 [Debug] AWSURLSessionManager.m line:542 | -[AWSURLSessionManager printHTTPHeadersAndBodyForRequest:] | Request body:
{"TableName":"SampleTable"}
2016-06-23 16:57:05.844 AWSiOSSDK v2.4.3 [Debug] AWSURLSessionManager.m line:552 | -[AWSURLSessionManager printHTTPHeadersForResponse:] | Response headers:
{
    Connection = "keep-alive";
    "Content-Length" = 125;
    "Content-Type" = "application/x-amz-json-1.0";
    Date = "Thu, 23 Jun 2016 07:57:05 GMT";
    Server = Server;
    "x-amz-crc32" = 2088342776;
    "x-amzn-RequestId" = FPM78JRBQIKG2DOLI62SL4IRMFVV4KQNSO5AEMVJF66Q9ASUAAJG;
}
2016-06-23 16:57:05.845 AWSiOSSDK v2.4.3 [Debug] AWSURLResponseSerialization.m line:63 | -[AWSJSONResponseSerializer responseObjectForResponse:originalRequest:currentRequest:data:error:] | Response body:
{"__type":"com.amazon.coral.service#MissingAuthenticationTokenException","message":"Request is missing Authentication Token"}

也许我错过了如何使用身份验证令牌 . 我的代码出了什么问题？

谢谢 .