Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.
I get quite a few request to join from public documents I own.
I realized we display the share button even for users who aren't loggued in.

Describe the solution you'd like
Do not show that button to unauthenticated users.

Describe alternatives you've considered
The future look of public pages will be associated to publish to the web #1650
I hope it will reduce confusion for users.

Discovery, Documentation, Adoption, Migration Strategy
If you can, explain how users will be able to use this and possibly write out some documentation (if applicable).
Maybe add a screenshot or design?

Do you want to work on it through a Pull Request?