I want to use the AWS Sdk 2 write a iOSapp, prepared by using Cognito on Facebook and Google and DynamoDB to associate authentication,

"ResumeSessionWithCompletionHandler" run well at first, but after about an hour, when I try to request DynamoDB under Cognito temporary token, has received the notice of abnormal token expires,

Exception message is as follows:

Error Domain=com. Amazonaws. AWSDynamoDBErrorDomain Code=0 "The operation couldn 't be completed. (com) amazonaws) AWSDynamoDBErrorDomain Error 0.)" The UserInfo=0 x7bf3a280 {message=The security token that included in The request is expired, __type=com. Amazon. Coral. Service# ExpiredTokenException}

How to deal with overdue token?

AWSCognitoIdentityProvider seem to have a "update" method, and can't through it to get a valid token?

Who can help me to look at how to solve? Be urgent! Thank you very much!