the Chinese name of user agent is user agent, which is abbreviated as UA, and it is a special string header, which enables the server to identify the operating system and version, CPU type, browser and version, browser rendering engine, browser language and browser plug-in used by customers. Some websites often send different pages to different operating systems and different browsers by judging UA, so some pages may not be displayed normally in a browser, but detection can be bypassed by disguising UA.