As network analysts, we can use a network protocol analyzer tool like Wireshark to inspect HTTP traffic and retrieve the username and password from the http://testphp.vulnweb.com/ website.
Wireshark is a free and open-source network protocol analyzer. It is used for network troubleshooting, analysis, software and communications protocol development.It can capture packets from a network connection in real-time and display them at a granular level. Once these packets are broken down, you can use them for real-time or offline analysis.