ios - DynamoDB iOS 示例权限错误

Question

我正在尝试使用 AWS here提供的 DynamoDB 示例，但我遇到了这个错误：

2014-12-17 11:26:32.374 DynamoDBSample[8952:766429] AWSiOSSDKv2 [Error] AWSCredentialsProvider.m line:433 | __40-[AWSCognitoCredentialsProvider refresh]_block_invoke293 | Unable to refresh. Error is [Error Domain=com.amazonaws.AWSSTSErrorDomain Code=0 "The operation couldn’t be completed. (com.amazonaws.AWSSTSErrorDomain error 0.)" UserInfo=0x7f8fdb82fd20 {Type=Sender, Message=Not authorized to perform sts:AssumeRoleWithWebIdentity, Code=AccessDenied, __text=(
"\n    ",
"\n    ",
"\n    ",
"\n  "
)}]

我对 Auth 和 UnAuth 的 IAM 政策是：

{
"Version": "2012-10-17",
"Statement": [{
    "Action": [
        "mobileanalytics:PutEvents",
        "cognito-sync:*",
        "dynamodb:*"
    ],
    "Effect": "Allow",
    "Resource": [
        "*"
    ]
}]
}

我有点坚持下一步要尝试什么。请帮忙！谢谢