Description:http://www.megabeets.net/wp-admin/profile.php
Watch your heads!

The description is telling the whole story. Simply look in the response’s header and you’ll find the flag. In order to do that open the browser’s Developer Tools (F12), bring to focus the Network tab and click the challenge. The HTTP requests will show up on the left panel. Select the request and the Flag header will be displayed on the right panel.

 

Decode the string with base64 and reveal the flag.

$ echo QVNJU3szMWE0ODM5MDBiODU3NjQyNmNjY2RmNTU0MDJiOWRkNn0K | base64 --decode
ASIS{31a483900b8576426cccdf55402b9dd6}