kemono works by people buying the subscription to share the content they can see some patreon pages. If it's just image files; it's always obtainable this way. Just wait for someone to upload them there, or be the hero and do it yourself.
If it's a program that runs on your computer, it's possible but you'll need some decompilation knowledge. Typically you'll need to see which variables change when your authentication is successful and adjust them accordingly.
If it's a program that works fully server-side, there isn't much possible way unless an XSS of some sort is possible on the site; which in that case the site owner has bigger problems than some rando trying to pirate their program.