当用户在AWS Cognito中的访问令牌过期时，需要使用AWS Cognito SDK或REST API发出新的令牌请求以获取新的可访问资源的令牌。以下是AWS Cognito SDK中的示例代码：

// Using the AWS SDK for JavaScript const AWS = require('aws-sdk'); const AmazonCognitoIdentity = require('amazon-cognito-identity-js');

const poolData = { UserPoolId: 'YOUR_USER_POOL_ID', ClientId: 'YOUR_APP_CLIENT_ID' };

const userPool = new AmazonCognitoIdentity.CognitoUserPool(poolData);

const userData = { Username: 'YOUR_USERNAME', Pool: userPool };

const cognitoUser = new AmazonCognitoIdentity.CognitoUser(userData);

const authenticationData = { Username: 'YOUR_USERNAME', Password: 'YOUR_PASSWORD' };

const authenticationDetails = new AmazonCognitoIdentity.AuthenticationDetails(authenticationData);

cognitoUser.authenticateUser(authenticationDetails, { onSuccess: function (result) { const accessToken = result.getAccessToken().getJwtToken(); console.log('Access token: ' + accessToken); },

onFailure: function(err) { console.log(err); } });

在以上示例代码中，AWS SDK for JavaScript和AmazonCognitoIdentity.js库被导入并用于创建用户池和Cognito用户。用户池ID和应用程序客户端ID在poolData对象中设置。用户数据和身份验证数据在userData和authenticationData对象中设置。最后，通过调用cognitoUser.authenticateUser函数来进行身份验证。如果验证成功，就会返回新的访问令牌。