Trying to desensitize and tame a hissing, feral cat, whether kitten or adult, can be a slow business. You can speed it up immensely with the clicker.
Use a highly-preferred treat, such as canned tuna or any freeze-dried fish cat treat. Approach the cage, let the cat retreat, put a pea-sized treat in the front of the cage, click, and instantly back away. You are giving the cat two kinds of benefits: a) food comes and b) scary person backs off. Give the cat a minute or two to eat the treat. Even if the cat does NOT eat the treat, by the third repetition it will be learning that Click means you're backing off.
Leave the cat for an hour or more, then repeat the process; this time, watch for the cat to take a step toward the front of the cage. Click that paw movement as it happens, then place the food and step back. Repeat. The cat is now â€˜controlling' both the arrival of food and the departure of person, by coming forward. This gives even the wildest cat great confidence and a feeling of safety. Soon you will not have to step back, and the cat will be on the way to learning what good company humans can be.