Allow to add public shared folders to be used on clients

[tobiasKaminsky]

• [ ] Android https://github.com/nextcloud/android/issues/9652
• [ ] Desktop nextcloud/desktop#4133
• [ ] iOS

TODO

• [ ] test normal share with write permission
• [ ] test read-only
• [ ] test file drop
• [ ] test with password protected
• [ ] test after expiration date

To discuss

• [ ] what to do with "hide download" enabled

Someone shares you a folder via public link and you want to interact with it. Currently you are limited to use web only.

Idea is now to allow all clients to add this public link and use it like a real account

• click add public link
• enter url
• now you can change between your real Nextcloud accounts and those public shares
  • browsing on mobile
  • uploading
  • even auto upload files into it

On server (and thus then a separate issue):

• on all public shared folders offer "add to clients"
  • via e.g. special nc://share/ protocol clients can directly add it

This is first a rough idea, some things are to consider

• how to check/show if a share is not available
• proper handle read-only shares
• do not allow re-shares

[tobiasKaminsky]

How to test:

• create a public share, e.g. http://localhost/nc/index.php/s/FEWZKfQ4g3Lsay2
• use cadaver (or any other webdav tool) and connect to: http://localhost/nc/public.php/webdav
• username: FEWZKfQ4g3Lsay2
• password: as specified, blank if not needed

[tobiasKaminsky]

Related on server: https://github.com/nextcloud/server/issues/16305

[jancborchardt]

There will be a new link in the server on the share link page, as specced in https://github.com/nextcloud/server/issues/16305#issuecomment-1005653162

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And then on click, the following modal can show in the desktop client / Android app / iOS app:

Sync share from [instance domain] Do you want to sync the folder [folder name] shared by [sharer name] with your [desktop client / Android app / iOS app ]? It will be added as a folder separate from your existing accounts.

Buttons: Sync share / Cancel

If the share is password-protected, there would be an additional section:

This share is password-protected, please enter the password: [ Password for share ]