AWS Cognito 是一种托管的用户身份验证服务，可帮助开发者轻松地添加用户身份验证和授权功能到应用程序中。下面是使用 AWS Cognito 进行用户登录和令牌刷新的代码示例。

1. 安装 AWS SDK for JavaScript：

npm install aws-sdk

2. 创建 AWS Cognito 实例：

const AWS = require('aws-sdk');
const { CognitoIdentityServiceProvider } = require('aws-sdk');

const region = 'your_aws_region';
const userPoolId = 'your_user_pool_id';
const clientId = 'your_client_id';

const cognitoIdentityServiceProvider = new CognitoIdentityServiceProvider({ region });

3. 用户登录：

const login = async (username, password) => {
  const params = {
    AuthFlow: 'USER_PASSWORD_AUTH',
    ClientId: clientId,
    AuthParameters: {
      USERNAME: username,
      PASSWORD: password
    }
  };

  try {
    const response = await cognitoIdentityServiceProvider.initiateAuth(params).promise();
    const accessToken = response.AuthenticationResult.AccessToken;
    const refreshToken = response.AuthenticationResult.RefreshToken;
    console.log('Access Token:', accessToken);
    console.log('Refresh Token:', refreshToken);
  } catch (err) {
    console.error('Login Error:', err);
  }
};

login('your_username', 'your_password');

4. 刷新令牌：

const refreshTokens = async (refreshToken) => {
  const params = {
    AuthFlow: 'REFRESH_TOKEN_AUTH',
    ClientId: clientId,
    AuthParameters: {
      REFRESH_TOKEN: refreshToken
    }
  };

  try {
    const response = await cognitoIdentityServiceProvider.initiateAuth(params).promise();
    const accessToken = response.AuthenticationResult.AccessToken;
    const newRefreshToken = response.AuthenticationResult.RefreshToken;
    console.log('New Access Token:', accessToken);
    console.log('New Refresh Token:', newRefreshToken);
  } catch (err) {
    console.error('Token Refresh Error:', err);
  }
};

refreshTokens('your_refresh_token');

以上代码示例演示了如何使用 AWS Cognito 进行用户登录和令牌刷新。请确保将 "your_aws_region"、"your_user_pool_id"、"your_client_id"、"your_username"、"your_password" 和 "your_refresh_token" 替换为实际的值。