Sewer Keys | Act III - Karthal MMX: Legacy Guide

For the break into the garrison to be successful, Hamza expects you to steal the key from one of the Black Guards named Theron. Without the key, you can forget all about sneaking your way into the prison. Hamza only knows his name, but he does not know where to find him.

An inn in the Slums run by a... Wizard?

You will find him in the inn(1), which is located in the Slums. You will not even have to fight so, casting protection spells, before you enter, is not necessary.

The only thing that you need to do is to enter and buy the man a drink and he will fall to the ground drunk. Not too strong head, it seems. Run through his pockets and take sewer the key.