You need a file from a victim's linux server. You had managed to look through his notebook containing his password of the machine. But you still need his username to SSH into the machine and steal that file. The victim's son Joe is 15 years old. He has recently started learning PHP and is interested in the IP of various servers. So he has made a simple PHP client that get's the IP of a server if you provide the domain name. Being a beginner he might have left some security bugs untouched. Luckily he has hosted his page on the same server. See if you can find something interesting in the page.
Here is the link to the webpage.
Flag is SHA-256(user_name);