"Play as guest" button does not work

[Nightcaat]

[y21]

I added the "backend" label to it (and to the backend project) since it wont work even if we fixed the frontend part (unless you want to display an error such as "playing as guest is not available for now", should probably have been more clear when submitting the issue).
Here's what I mean: /app/ requires a sessionid GET parameter and sessions only work for users since a session id is stored with a username row. We could pass null for username, but then we would not be able to differ between guests.

[y21]

The guest button works now.

[Nightcaat]

It still doesn’t work on the registration page.

[y21]

Oh sorry, I didn't realize you reopened this. I will add the "Play as a guest" on the registration page as well.