When you enter the page for the first time, you will just see an input to enter a PIN. When you enter the wrong PIN, it fails silently and just reloads the page. If you enter the right PIN, it will save a cookie access and shows you the welcome page.
Then I will simulate that I previously entered the right PIN and have a cookie that lets me pass.
You may replicate by just running the tests above and go through the errors yourself.