after you startup your tomcat, you type a concrete request url in broswer, the tomcat probably will prompt you the subsequent message.
it is because the <security-constraint> will restrict the access and in need of authentication.
please comment this tags in web.xml file of directory WEB-INF of your webapp. it will help you to solve the issue.
http://localhost:8080 is requesting your username and password
原文地址：https://www.cnblogs.com/daniel123/p/8572761.html