要使用自定义UI，需要在Cognito User Pool客户端设置中指定自定义UI的URL，并在Web应用的代码中调用该URL，而不是调用默认的托管UI。例如，在React应用程序中，可以在登录组件中使用以下代码来调用自定义UI：

import React, { useState } from 'react';
import { CognitoUser } from 'amazon-cognito-identity-js';
import { AuthenticationDetails, CognitoUserPool } from 'amazon-cognito-identity-js';
import { Redirect } from 'react-router-dom';

const SignInForm = () => {
  const [username, setUsername] = useState('');
  const [password, setPassword] = useState('');
  const [redirectToReferrer, setRedirectToReferrer] = useState(false);

  const onSubmit = (event) => {
    event.preventDefault();

    const authenticationData = {
      Username: username,
      Password: password,
    };
    const authenticationDetails = new AuthenticationDetails(authenticationData);

    const userPool = new CognitoUserPool({
      UserPoolId: process.env.REACT_APP_COGNITO_USER_POOL_ID,
      ClientId: process.env.REACT_APP_COGNITO_CLIENT_ID,
      RedirectUriSignIn: process.env.REACT_APP_CALLBACK_URL,
      responseType: 'code',
      scope: 'email openid profile',
      CustomDomain: process.env.REACT_APP_COGNITO_CUSTOM_DOMAIN,
      UserPoolDomain: process.env.REACT_APP_COGNITO_USER_POOL_DOMAIN,
      AdvancedSecurityDataCollectionFlag: false,
    });

    const cognitoUser = new CognitoUser({
      Username: username,
      Pool: userPool,
    });

    cognitoUser.authenticateUser(authenticationDetails, {
      onSuccess: () => {
        setRedirectToReferrer(true);
      },
      onFailure: (error) => {
        console.error(error);
      },
    });
  };

  if (redirectToReferrer) {
    return ;
  }

  return (
    

       setUsername(event.target.value)} />
       setPassword(event.target