You just log into your patreon (just in another tab like you would normally do). then ingame you click top right, authenticate. it will make a pop up like you know it from many other sites and ask you to allow it to connect your patreon. You need to be a follower tho - else it won't work.
You can't leave the window while it's unlocking - you have to wait for it to unlock the Character. It will work if you click it again and wait for a few seconds.
