Trying to get the needed username. I think I know what to do, but because of the WAF I cannot reuse any code, but instead need to write my own.
This part is really frustrating… If anyone has gotten the needed user to login the intended way, could you PM me, so I can check if my script is correct?
Nice learning experience so far though. 
Edit: Finally got user!
This was really tough. I liked the part to get user though. Really made me look deep into a lot of things a never really even thought about.
Thanks to @MinatoTW and @egre55 for the painful, but awesome experience so far.
Root must wait till tomorrow… This was really exhausting.
Edit 2: Got root!
Really interesting walk through AD.
However, the box has a bit of a design-flaw so that it can easily spoil other users…